One of those AC Cobra reps would be my way to go. They are awesome!!!
As far as maintaining value or even gaining value, usually they have to be completely original which means that tracking the car is out of the question. However, I have been noticing that well completed project cars are holding value as well. You can always pick up a nicely built camaro / corvette that can handle track duty but like I said, those cobras are fantastic!!!
I'm sure you know but I mind as well say it, check out
http://www.pro-touring.com/forum.php
My dad built a '67 pro touring camaro that I beat on so I may be a bit biased when it comes to this stuff...