What's a survey cost? A $1,000? The worst that can happen is you spend $1000 and save $10,000 if there are too many warts. The upside is you effectively spent $12,000 for a boat you can live with. 

Some advice that I was given was to buy the best boat that I could comfortably afford - something that had been really well maintained. Unless you prefer working on a boat more than sailing her, you might want to follow that advice. On a boat that age that wasn't maintained, everything will need replacing or fixing, and when you are through, you'll still have a 30 year old boat.

Anchor rode, windlass, depth meter, GPS, engine, running rigging, standing rigging, thru-hulls, wiring, stove, sails, cushions, water system, gel coat, core (moisture level), chart plotter, shaft, prop, furling, canvas, lifelines, steering, clutches, batteries, switches, holding tank, VHF, battery charger, autohelm, blisters, keel, hoses and clamps, ports, stainless, wood interior, stove, leaks, lights (running, anchor, steaming, interior), transmission, fuel system, hull and deck joint, stuffing box, refrigeration, accumulation of bottom paint - and much more!

You can survey a lot of that yourself (blisters disappear after being out of the water).  If you like her, you can continue the process, but you still won't have a swim platform, etc., etc. Even after being surveyed, will you trust her?

We spent more on Southern Comfort than we did on any of our houses except the one we are living in, and I've never had a day of buyer's remorse.

Dick

Random thoughts:  How much time do you have for all the work you describe? And the surprises to come.  Do you have the skill set to do the work correctly? What value do you put on your time?  I think you can buy a MUCH better same age Catalina 30 for a few thousand dollars more $15-20 K) and save yourself much aggravation and actually do some sailing.  (Yes, I know the boat you are looking at is a 36 foot Catalina).  Keep in mind keeping boat on the hard at a marina isn’t free.  Plus you have to insure the boat too.   If you or your sailing partner have allergies, a boat like this will have hidden black mold and the interior cushions will all need to be replaced.
Some times the best deals are the ones you walk away from.

Do not waste your money on a survey, which will only confirm that $11, 000 is a gigantic gamble.A survey will only uncover the major shortcomings that will be obvious That list will by no means be a complete list of the repairs that you will need to do. That boat on the hard is costing the owner a lot of money that his wife is probably furious about.  He would love to get rid of that albatross.  You, on the other hand, need to decide whether you want a two or three year project (or longer), or do you want a project that you can sail and work on at the same time.  You're probably looking at $50,000 in updating and repairing, plus the years out of the water.  Consider that even a newer boat is going to require your constant attention, and a constant outlay of cash to maintain.  It's a romantic idea that will most likely end up with you trying to unload that albatross.  Actually, there are a lot of boats out there whose owners kept up nicely and are selling due to a number of issues: nonuse, health, or aging, etc.
Sailboats are for sailing.  Get one that floats and doesn't need new everything. $50,000 to $60,000 will buy a much nicer and newer boat.Now, I realize that you may not have that kind of money laying around. Start saving!   I would get a survey on such a boat. 
Just my 8 cents.

I wouldn't hesitate to buy an old Catalina sailboat only if it is in good condition and being used regularly.  Last year I sailed my 1990 C-36, Caprice, to Cuba and had gust up to 38 mph with 12 foot waves in the Gulf of Mexico at night. The only problem we had was Sea Sickness. On the way home we did have a miner electrical problem that was quickly  found and repaired underway by the crew. If you do buy any sailboat change the the fuel filters and the oil and filters. If it is old replace the fuel tank or cleaned in addition to all the rigging lines and stays also everything else that does not look good.  I bought an old sailboat years ago that was sitting on the hard neglected for three years. I replaced the above and cleaned it up then sailed it for five years. Back then I was young and liked working on boats while having a beer or two.. Now that I am 81 and retired all I want to do is sail  my 1990 C-36 which is at my dock behind my house here in Florida. It is easy to maintain and sail single handedly.  Life is good.

I have a '87  C36 tall rig so some experience with a boat of similar age.  Our Boats built back then had one big weakness and that was where the chainplates go through the deck.  Catalina just cut through the deck leaving the plywood coring next to the chainplate.  Lack of very vigilant maintenance resulted in water entering the deck core. Check the bulkheads beneath the chainplates, the leaking can compromise them as well.  big pain to replace.

So my first advice is to borrow or buy a fiberglass moisture meter.  I bought one out of canada for about $150.  works great once you teach yourself how to use it.  way cheaper than one failed survey.  when ever you look at any boat run the meter over the whole deck and watch the salesman or owner's face.  For the Catalina use the deck coring layout (I posted one on here a few years back) and write in your readings.  If there is moisture or delamination in the core you'll find it.  Be sure and do the cockpit sole around the pedestal as well.

I don't have a view on older / newer.  In the end you buy what you can afford and what you have time/skill to maintain or repair.

As far as upgrades cost I can say a new set of cruising sails set me back about $3200.  A new roller furler was $1200 plus labor (Harken had a great upgrade price).  A new headstay was around $500 including labor.  A new set of lifelines was around $600 if I remember right.  If you have access to a crane to pull the mast yourself you could order a new set of rigging pretty reasonably. figure on replacing most all of the electrical system.  Battery selector switch, batteries, battery cables, most of the light fixtures (the old plastic ones fall apart with age), charger, pumps. figure the water heater won't work and if they installed an electric fridge in the old icebox it probably didn't work very well when it was new.

you can roll new gelcoat mixed with non-skid over the old non-skid areas to spiff up the deck. cracks are a bigger pain to repair.  If the boat has been on the hard for years then the hull should be dried out and you can either peel the gelcoat on the bottom and then recoat or take your chances and epoxy barrier coat and hope the blisters don't come back.  

cushions can be a big expense but the rest of the interior can pretty much be cleaned up, revarnished or painted.  Just watch out for rot in the cabinetry. 

Other than that, if the engine and transmission are good all you really need to do is add all the cruising extras you want.

Project boats are all about the time and money.  This one is going to need tens of thousands (mentioned above at about $50k) to bring it up to top notch shape.  The '86 Cat 36 "Suzie Q", owned by a retired navy admiral and fitted out like a new boat, sold for about $50k USD three years ago and it was in ideal (like new) condition.  I fully updated a 1978 26' Mirage that had been somewhat neglected and it took me 5 summers of non-stop work every weekend (ALL weekends) and cost me maybe $15k in parts and materials.  This one is going to be an intense, long-term, labour of love.  He really should pay you to take it off his hands, or sell the motor alone for $5k and scrap the rest, sadly.  Many such boats go to single guys like I used to be while working on the '78 Mirage and become hobby projects lasting a decade or more. 

For perspective we ended up with a 1991 Cat 36 in good shape for $43k USD back in 2013 that had been on the hard for over a year.  We've put in another $20k in minor upgrades and fixes (new canvas, upholstery, alternator, water heater, electric head, etc.) and every year brings another $5k in desired and required upgrades and a many weekends of solid labour.