How about turning the "Brains" into more of a game itself.

For example - How about a reward of 1 brain for each tournament game win, and also give brains as reward for winning a tournament (more brains for bigger tournaments). Or also when you have site tournaments offer extra brains to the winners.

Then instead of having brains buy memberships - have a whole "store" of things that can be bought for brains. (And when I say "store", mostly fun things that will not cost BK anything)

For example, some of the things that could be in the store: (Again, just examples - and example amounts)

10 Brains - You can make a post in a different color

10 brains - the background of a post can be in a different color

20 brains - lets you do both background & font different colors

50 brains - You can turn in for an extra vacation day

100 brains - You can turn in to get an APPROVED picture added to your profile

200 brains - you can get your rook membership expanded by 1 month (2 month Knight)

1000 brains - Let you post an APPROVED message to system news to stay for everyone to read for 2 days.

etc... etc...

The only down side would be that some people who be more prone to cheat to get more "brains" - but would be a cool extra feature.

Also - for Paid Members only - giving pawns another reason to join!