The main reason I see in going to 700s is that you will have alu rims which will greatly increase your braking power. Steel rims do not brake very well when dry, even with better pads, like Koolstops, etc, and braking is almost non-existent when wet. I've learned to live with the braking issues on mine.

But I agree with the others that it doesn't make a whole lot of sense to spend big bucks on wheel upgrades for a bike you can get at thrift shops or Craigs for around $50.