any car can be built up, but some platforms are just a lot easier to work with and can have greater potential. usually depends if money is an issue, or if you love a certain auto too much! (like me wanting to eventually make my LX into a WRC worthy vehicle...lol won´t happen for a loooong time :-] )
also, building up cars no one expects you to turns them into sleepers...
just be cautious and try not to overestimate your gains. g´luck! ;-)