I know it sounds weird, but there can be a great sense of exhilaration inactually WEARING OUT bike parts instead of just upgrading... I had a pair of MAVIC CPX22 semi-aero rims with 105 hubs on my first Kona Jake. I rode the HELL out of that bike to the tune of 4500 miles in 3 years.


Now remember, this is a silly older guy's rants and raves. Obviously you canmake a decision that is both financially responsible AND practical, but just don't get in too much of a hurry to replace perfectly good parts.
Speaking of spending money, have you been professionally fitted to your bike? That's a GREAT way to spend about $100 and actually have someone analyze your pedal stroke and ride position...
Another thought: spending big bucks on well made, folding-bead (Kevlar)tires and latex (light) tubes can actually make a big difference, and I can guarantee you that a 105 level bike probably came with cheap-ass tires... I put new tires and tubes on my Litespeed, and it felt like I got brand new wheels(seriously). A steel bead and a butyl rubber tube is a good bit of rolling weight to have to get up to cruising speed where as a latex tube and a Kevlar tire feels like it has a bit more "get up and go" in initially spinning up.
These are a great example of a truly well made tire:
Continental Grand Prix 4000
http://www.coloradocyclist.com/product/display/25110/
Boy, I can just ramble on forever... Bikes are just too much fun.







