1. Trading Store ("Arms Dealer"?) -- ability to trade R, SR and UR units with the store possibly for game currency cash or gold. If this was done with GREE acting as the "merchant" intermediary for all the transactions it could potentially be revenue generating making it worthwhile for GREE/MunkyFun to invest development time. Alternatively this could be operated on a consignment system where players offer up a unit for one or more acceptable payments. (Example: Player offers 1 SR Attaturk III for either 200 gold, 1 UR TWA Corbies, or a UR Fumigator in return.)
2. Global Chat or Much Improved Alliance Recruiting System -- A global chat is the simplest method of dealing with the recruiting problem. It's what other developers commonly employ and it's a tool right out of MMO's where clans/alliances play a major role. Alternatively a recruiting system almost like big wall with advertised openings (this would be a big improvement over the small list selection presented now. This system would involve more development than a global chat. But both would help build the relatively lacking social aspect of the game.
3. Offline Alliance Communication (History) and Private Messages. Again the chat features in this game are very limiting. It's very difficult to communicate with members who aren't always online at the same time. One game I played on iOS employed 3 chat modes (global, alliance and private) plus an email like system to send messages to offline alliance members. This worked beautifully. I would love to see at least some effort to improve communication. Even having some persistent history (last 24-48h) in the alliance chat would be an improvement. This shouldn't have too much of a data overhead cost.
4. Big events -- advertised in advance, bigger prizes -- maybe a Christmas Gold Key Bonanza. GREE/MunkyFun could monetize this by selling booster packs -- the goal being above average participation. This should be a once in a while thing (maybe find like 4x a year to run events like this.)
Developers, feel free to PM me (or have Tadaaah do it) if you want any info.