Well so what are we discussing here? I thought we were talking about the cars of todays era, that one day will be popular to modify when their price goes down.
Skylines were hardly cheap when they first came out ($60,000+ for a GTST, $100,000+ for a GTR).
Also modern cars don't need you to 20 mods just to get 50% more power over factory. A slight flash tune, exhaust and intake upgrade is usually all that is needed out of any modern V8 or turbocharged car.
Personally, "tuners" cars aside, i'm looking forward to second hand supercars prices coming down in 10 or so years time. Something like a 05 F430 or a 03 Murcielago dropping to around $100,000-$150,000 will make them very realistic to own.