I'd back up bsyptak.

No sense in replacing functional stuff with similar, slightly better (?) stuff at great expense. Also consider re-sale value. You are highly unlikely to get a lot more for your bike with an upgrade - certainly not what you laid out for the components.

However, if you replace stuff that's worn out I don't see any harm in getting better stuff, especially if you plan to keep the bike. If it fits you well and you like it, just ride the bejeezus outta the thing and treat it to some upgrades when replacing whatever needs replacing.

Another benchmark; if the upgrades are so expensive that you could just waltz into a shop and buy a new bike with same quality frame and components for the same $ - or less (highly likely since you will always pay more for parts retail than a manufacturer will) it clearly makes more sense to just sell your old bike and put the money towards the new one (or keep the old bike for a winter/beater/trainer).

Frank Berto wrote a great book on upgrades , out of print, alas, but worth hunting for: http://www.thedancingchain.com/More%20Books.htm

The components he tested are long obsolete (6 & 7 spd drivetrains) but the book is solid on upgrade logic and worth reading.