Keep them on the bike as long as you want, or care too. They will stop the bike fine, especially after you change to Kool-Stop Pads. Eventually you will get upgradeitis and then you replace them, long long after you go to a better wheelset, cranks, etc etc. Brakes, were the last thing I upgraded. If you never uprgrade them, you'd never notice much difference in the end. If you get weight-weenish then they eventually come off.
If you change them out, just keep them as a spare. You'll won't make much $$ on them and it would better serve to have a spare brake set just in case. I sold off my old brakes to a bud, and when I sent my Zero G's in for upgrading, I was without brakes, and so bike, for a week.