FWIW & IMHO:
I held out keeping my '87 turbo-t bone stock for as long as possible, which was about 15K miles or so. I have done Walbro, Racetronics hot wire kit, Sylvania Silver Stars, SS THDP & TH 2 way cat, Hooker cat-back, Hooker Aerochamber muffs, Accufab, Bilsteins, Neal Steward street chip, 200 amp alternator, mini-starter, Scanmaster. So far. Current mileage is 16.6K or so. Some of these were wise moves, and a few so-so. I don't think that modding a car hurts the value as much as it appears at first glance. If you stick with wise moves, you might be suprised. One of the things that hurts the value of a modded car the most is that they are generally not sold till they are beat. Of the 33 cars for sale on E-bay currently, the first 4 are repeated twice. And the adds that you see under the GN classification probably are including most of the Turbo Buicks for sale on E-bay. As time goes on, expect to see fewer and fewer ultra low mileage, well equipped, '86-'87 Turbo Buicks for sale. No flaming intended. having to work at keeping the mileage down to keep he value up is pretty self defeating, so to speak. There is nothing wrong with a garage queen, but the money in a bank in a simple interest saving account will bring more profit without the worry of whether your car will get stolen of it is increasing in value. The ideal situation is to have enough money to buy a garage queen and then use it. Spend it, cuase nobody else is going to appreciate it like you do.