I am relatively new to cycling. I purchased a Giant TCR C3 last summer and I have put about 4000 miles on the bike. Lately I've been increasing my mileage; I've gone from about 100 - 120 miles a week to 150 - 200 miles. When I purchased my bike I remember the owner of shop telling me it was a great frame but he considered the wheels (Xero X-3) and the brakes (Tektro) to be sub-par as compared to the bike. That has stuck it my mind since I purchased the bike and I am now at the point where I am thinking about upgrading the wheels and the brakes. I am looking for a little advice about the wheels in particular. I started to look a little bit online just to get an idea of cost and I was stunned to come across a set that cost almost $1500. What is it that constitutes a good wheel? Is it simply weight or are there other factors? I need a little education.