Magazines are the most neglected part of any handgun. They need regular cleaning just like the gun itself does. Pay particular attention to the followers because they will collect residue and begin to hang up. I usually soak my springs and followers in Hoppes and then clean thoroughly with a toothbrush. Then wipe clean. The inside of the magazine is also cleaned with a bore brush with hoppes, and then dried and wiped clean. The follower is the only thing I put oil on when I put the mags back together. Also, be sure to check the followers for gouges, nicks, etc and be sure to smooth them out before putting them back together.
On another note, the mag springs are rated for many thousand rounds, but if you feel they are getting weak, by all means, replace them.