I think the incentive to organise more MG events would be a good measure to implement for your community. Overall I think the MG server has a little potential left and needs people to look after it.
Other than that...
Cutting down the shit maps on the server would be a good begin, there are a lot of server killing maps on the server. The server has a lot of maps on it and this includes disconnect inducing maps and maps that need more players (all the deathrun maps). More than often one of these maps get voted for and there goes your population after a little while.
Currently my thoughts, maybe it's too much work for you, who knows but at least organise some more events, I think these can be quite fun.