XP is a feedback system, and it may be fun, and it well in practice "reward" those who post early, but so what?
XP != Reputation
I like to be believe that anyone who sticks around here for a while will come to know and respect others by the value that others' posts add, not the number of points that have accrued.
It's not XP that's going to get you invited to join a project, co-author an article, or get together for a beer with someone when they're in town.
Besides, anyone who is seriousy in it for the XP can figure out ways to rig the system (like keeping a private collection of identities that can all be used to cast votes). Is it worth the effort to try to stop that?