Merit sources have an indirect (unplanned) incentive to spend their merit.
We are more likely to receive merit in return for passing out our own merit. :/
I think that most merit sources do not need any merit.
Actually merit sources should not need merit at all. To avoid conflict of interest.
Anyway I think there is no need for an incentive.
Maybe we need more merit sources, because there are lots os comments daily in this forum and just a few (about 80 last time I saw) cannot read all of them.