If you modify the hell out of a car, you will never get the money you put into it, and the only person who MIGHT even give you slightly above blue book is someone who would want those same exact mods. Case in point:

My 2000 Prelude is completely stock (only a K&N filter) with 135,000 miles, no rust (I keep her clean as I can), and any work I've done I done with OEM Honda parts (belts, brake pads, water pump, stock replacement Bridgestone tires). I've checked around and when I'm ready to sell it I could get around $10,000.00 - even with that kind of mileage.

If I had half the mileage, it would go for $14-16,000.00

The same Prelude modded to hell like that with half the mileage would be lucky to sell for $8500.00