I have a 2010 GT Tachyon 3.0 I got for $450. It's got parts I can swap in and out on it--I have the original seat post, pedals, etc, even though I've upgraded some stuff.
I'm thinking of changing the crank and such ... in the future I may want a 10 speed, front discs, etc as time goes by. More pertinently, I've considered looking through performance parts and swapping in some reasonably smooth bottom brackets and freewheels and such, just find all the places I can lower friction and upgrade all that. I still need to finish tuning my derailleurs first though, but after that it's all friction components and heavy rims to worry about, and upgrading that stuff can be expensive.
Is it worth building up as time goes on, or should I keep it simple and keep an eye out for something like a used Trek FX or such instead? I'm doing neither right now, just wondering if I should plan for the future in the mindset of "Upgrades" or "New Bike."
OH FOR ... somebody move this to the Mechanic's forum.