[WhiteOne]

Have you ever tried to find a bone stock car? Is it possible to find a stock Supra? Aren't they worth a lot more stock?
Modifying a car to "make it your own" can actually reduce the resale value and make it harder to sell.
Big dollars spent on a loud exhaust system makes you a cop magnet and limits your resale options.
I have never been able to leave my vehicles stock. I never got the extra money I spent back when I later sold said vehicle.
Leaving the car stock and spending the money on maintenance is probably the smart move.
I wonder how hard it will be to find an unmolested 135i 10 years from now.

[jkp1187]

Depends what you want from your car (or, indeed, from life, generally). And what kind of car, too -- I'm sure you can find a bone stock Toyota Camry without much hassle....

Cars are an expense, not an investment, so I don't think you should modify a car expecting that you'll be able to make money when you sell it later.

[Spook]

If you want to be totally fiscally responsible, you're probably not buying a 135 to start with. Also, depends on the mod. Suspension upgrades are not in the same category as a turbo boost.