Its a tricky one, because normally you want to buy a car thats been looked after and you feel hasn't been thrashed etc. Theres a good chance that if a car has a big exhaust / intake / lowered etc, that the owner has been caning it! Having said that - if you buy a 'sports car' there is a very good chance that its been hammered anyway - as thats what they're designed for.
I suppose it depends what you want it for. Some people would be delighted with a car with the above mods, as it would save them fitting them themselves... and save a few quid. I think generally though, the majority of people would opt for a standard car before a modded car.
The other thing is that you never get the value of the mods back when selling a car... so you're probably better taking them off and selling them seperately anyway - and selling a standard car!