Spend the money on good cycling clothes, shoes, pedals, tools, water bottles, or lights. Upgrade parts on the bike as they wear out. You'll probably outgrow the whole bike at some point, so it's better to invest in things that you'll keep after you change bikes. Buy things that'll let you ride more rather than obsess more over your bike. A two pound difference in bike weight only makes a few seconds of difference up the hardest hills you'll ever climb -- and it doesn't make any difference if you're riding in a group. If you absolutely need to buy something for the bike, get some nice tires.