Also I should mention that some things in the past were made to last very very long unlike some modern and contemporary objects which are good to throw up after less than a decade. In the past there were less electronics and assistances in cars than there is now and it was much easier to repair them because the engines had carburetors and were not fitted with multi point injection. However Germany made the top quality electronic fuel injected V8 and V12 engines from the 80's to the 00's along with Cadillac Northstar V8 and Chevrolet Lt1 and Lt5.
Even for transmissions, back then in the 60's-70's-80's, there was no sequential electronic transmission but a good old heavy duty 4/5 speed manual like the ford toploader, mopar a833 and gm muncie m21/m22 rockcrusher or heavy duty 3-4 speed automatic like the torqueflite A727B, the gm hydramatic TH400 and the ford C6/lincoln/mercury cruisomatic which were almost indestructible. A good friend of mine Chuck Maddox said once:"Old tech that works is good tech." Then again when I look at Mercedes M116, M117, M119 and the M120 engines found in the w126 and w140 as well as for their BMW counterparts like the M70 and M73 engines respectively found in the E32 and E38, it just showed me that despite being designed many years ago these engines were and are very reliable and durable.
Same with older american made V8 engines from chrysler/dodge/plymouth family of big blocks including the 383/413/426max wedge/440 engines, lincoln with the 430 and 460 engines, mercury with the 406/428/429 engines, ford with the 390 code s/427code r/428cj/scj,428police interceptor/429scj engines, oldsmobile with the 425/455 engines, pontiac with the 389tripower/400/421sd,428sd/455HO/455super duty engines, buick with the 425nailhead/430/455 engines, chevrolet with the 396/409/427/454 engines and cadillac with 472/500 series of engines.These american made V8s are still running well and are still powering cars that are several decades old. You can easily find a lot of restoration spare parts as well high performance spare parts available which make them easy to repair and maintain.
Regarding Porsche, yes the 959 is not your average Porsche and you better have to know someone trustworthy if you want the car to be repaired perfectly.
Regarding value, just compare the vintage Rolex Daytona craze with the Muscle car craze especially with the prices of Hemi and 440/6 powered mopars, followed by 429 Boss Mustangs and 1970 Buick GSX Stage1s, 1970 454 LS6 Super Sport Ch'velles and 1970 455 HO Powered GTOs .Desirability, rarity and collectibility command those values. Also there is the problem with the auctions where the auctioneers allow the one with most money to over evaluate an item and win it. The result is mind blowing, one the few 1971 Hemi Cuda convertibles built sold for 3 millions dollars at a Barrett Jackson auction some years ago.
Like for everything else, if you want the car or the watch to work well, you have to have a serious eye on it and do proper maintenance. However some people think that because they buy a luxury car or watch, it will be cheap to repair, that is an enormous mistake. Before one buys something, he has to make sure that he can afford the costs to repair and maintain it over the very long run so that the watch/car will keep its value over the long run.
Just my two modest cents and have a good week end
Best regards
Georges