I've got a '06 Marin Fairfax, only upgrades are SPD pedals. I generally use it for daily commuting, 10 - 20 mi, and it works well for that purpose. Lately, however, I've started to ride with friends on longer 30 - 50 mi rides and it's a challenge to keep up. The people I ride generally have road/cyclocross bikes; I'm in excellent physical shape, but it's an constant challenge to maintain pace with them. So, I'm wondering whether there are cost effective upgrades to the Fairfax? Or, considering I paid $650 for it, is it better just to save my money and, eventually, just buy a new bike? (Saving my money is probably a 6 mo or more endeavour, which is why I'm interested in a cost-effective and appreciable upgrade).