Could and unmerit rule change anything? It could help even the higher ranks to stay more awake and want to mantain/earn more merits like the new users.
For example: If you don't earn one merit (or another form of reward) in a certain time, you lose one. One idea could be that you should earn a certain number of merits per month to maintain the others for example.
If this ever happen then this forum will be turned into a whining court

where there will be constant threads of cases from forum users demeriting eachother because of little disagreement or dislike. I am glad Theymos disabled that option.
It will be very surprising that people will use the demerit button more than the merit button because its somehow in people's nature to act in certain ways in getting back at people they don't like. And I agree, there are posts which are not getting the merits they deserve but what can one do; the world entirely is an unfair place. Everyone can't be pleased.