This kinda begs the question. When you have an engine that is over TBO, is it worth buying the plane, or should you just move on?
Trade-a-plane was offering a 152 that was fairly close to me (a 152) that had 2400 SMOH on the engine. Since their spec sheets showed that the TBO was 2400 hours I decided not to pursue the plane. Besides, the seller was asking the same price for a plane with a lot more time on the engine. For future reference, what should I do?
It's a crap shoot! A gamble! You pay your money and you take your chances! Sometimes you win and initially save big money on the purchase with a solid engine that will give you a few hundred more hours or a couple of years of trouble free service. But, that engine will sooner than later have to be rebuilt or replaced. You should have the finances in place to do that if needed almost from the day of the purchase. You're just as likely to loose the bet with a worn out barely airworthy collection of unserviceable parts that you wind up replacing at overhaul, if you can even get the airplane home first! Everything in life comes with risk, and only you know how much risk you can handle!
All things mechanical wear if we use them, and corrode if we don't! Catch 22! There's nothing wrong with buying a good airframe with a worn out engine (or shabby interior, or faded paint, etc.) but the purchase price has to be low enough to make repairs economically feasable. The engine can be overhauled or replaced, as can the interior, or virtually anything else. But, the basic airframe has to be solid! What should you pay for such a beast? Whatever the market says it's worth, and whatever you're willing to pay (in both time and money)! I know that's not much help, but it's simple economics. If you can buy a good airframe with worn out engine at a low enough price to make engine replacement/overhaul economically feasable, then it can be a great deal! You wind up with a good airframe and fresh engine at a fair price. If the seller wants so much that you could buy the same good airframe and fresh engine cheaper elsewhere, then you should go elsewhere and save the time and aggravation of restoraton!
The one thing that we all must find in an airplane to avoid financial ruin is a good solid airframe. If the airframe is good, Paint, interior, engine, exterior plastic ..... none of that really matters
if the purchase price is low enough, and we have the time and money to restore the aircraft; and then only
if it can all be done at a total price at or below market value for the
restored aircraft. You may even be willing to exceed market value in cost, in order to rebuild the aircraft the way you want it. Only your own market research, aquired knowledge, time constraints, and honest desire can help you make that final decision.
Airframe total time is one of the biggest variables in (perceived) aircraft value. There are pros and cons here, too, but basically you pick a market price range that you can afford, and you'll find a corresponding range of total times. These are the aircraft you will most likely investigate and consider purchasing. You should probably buy the lowest airframe time you can afford, but it usually doesn't really affect anything but purchase price and resale value, if you do your homework prior to purchase.
The number one destroyer of otherwise solid airframes is corrosion. Nothing else is as expensive to fix, or as hard to find before purchase. I have always said that all aircraft have some amount of corrosion, which varies from "can be wiped off with a dry rag" to "major airframe components missing"! This is your number one concern when buying an aircraft, and there are plenty of good airframes still to be had. You just have to be careful of the few bad ones, and know what is acceptable corrosion and what isn't.
Engine condition is second only to airframe condition, both for safety, and from an economic standpoint, and is not necessarily dependent on TSOH. A zero time engine is a bigger safety risk (to me) than one with a few hundred hours on it, and maybe even a bigger risk than a proven engine at TBO. Generally, the higher the TSOH, the more expensive the eventual overhaul will be, because more parts should be out of limits. An engine exchange with a reputable builder rather than overhaul may be the least expensive way to go on a very high time engine.
Repainting (when needed) is the next biggest expense to restore properly.
Avionics can be a huge expense, if the aircraft has old or obsolete equipment that doesn't meet your needs, and upgrading often only adds a small percentage of the cost to the market value of the aircraft. Installing the latest and greatest is something you normally only do to an aircraft you plan to keep for awhile, as you never recover the cost on resale.
Almost everything else is bolt on or cosmetic, and can be upgraded over time at reasonable cost, even if it sometimes adds little to the cash value of the aircraft.
In real estate, there is a growing group of investors who buy old houses and fix them up for resale at a good profit. It's called "Fliping" (I'm not talking about the late night scam artists who say they have a foolproof method to make you rich). There are similar investors in aviation (I'm a very small one myself). Some are careful about their product quality (I am), and others aren't so careful, but it is proof that good airplanes can be found at reduced prices that can be restored and returned to service at reasonable cost. (I'd have twenty in the hangar, if it were big enough, and I'd had the funds to buy them).
For some personally, buying an aircraft that is already almost exactly what they want is the only real option (and they'll tell you so). For others (like myself) that aircraft doesn't exist, and I will have to compromise and build what I want from what's available. Still others (I'm here, too) don't have the funds to buy a cosmetically attractive aircraft, and again have to compromise on appearance to have a safe but reliable ugly duckling! And that's OK! I enjoy my ugly duckling just as much as others enjoy their swans (and someday, mine will be a swan, too!)
So, should you walk away from a high time engine (or anything else)? Sorry! ........ It all depends on you!
(Sorry to be soooo long winded, but there is no simple answer, and there's a lot of ground I
didn't cover.)
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There is just a lot to think about. I have heard others say that it is the quality of the airframe and the engine that are important, not the quality of the paint. 
