spark plugs

According to my maintanance manual, I should have replaced my spark plugs 10,000 miles ago. The dealer will do it during the major service, but you pay close to $300 for a bunch of ish that can either be done yourself, or done cheaper elsewhere. Anyways, since I'm gonna change plugs, should I invest in performance plugs, or wait until after i/h/e? Will they make a difference? Are they woth the money?

Also, can plugs be easily changed yourself, Or should I pay some guy to do it for me?