A few ideas:
One problem seems to be the amount of time given to work on them. It seems every battle there's people who drop out due to time constraints or just don't even start simply because they think they won't have time to get anything done. So, maybe more time needs to be given for them? Turn it into a monthly map battle? Which leads me to my next point...
Another problem might be that people never know when a new one is starting, and can't plan for it in their schedule. So, building off the monthly map battle idea, have each new battle start on the first of the month and complete on the last day of the month. Easy schedule to remember. Which leads me to my next point...
Lag between battles. This gets me every time. I really get into a battle and get myself into that map-making frame of mind, having a blast. The battle ends, and boom! Nothing new for a couple weeks (or more.) Momentum lost, map-making fire extinguished. If they're only being done monthly, why not overlap them? One battle ends, the next begins immediately, and voting for the previous battle takes place for the first week during the new battle. No lag.
So, in short:
Monthly battles.
Always begin on the first of the month.
Always end on the last of the month.
More time to come up with new stuff, no wondering about when the next battle beings or the current one ends, no lag between battles. Less work for Barra and the other admins as the contests are less frequent. Win. Win. Win. Win.
Maybe also spotlight the winners map on the front page? Perhaps some front page fame-whoring will get some more people into it.
Plus, even if only four or five people participate in each one, that's four or five cool new maps to look at each time! I'd say that's pretty good! Plus, I think if it's run in a clear and consistent way, it could build up momentum over time and continue to grow.

















