Have ya'll thought about making it possible to trade players with anyone in the game or at the very least trade players with someone in a person's Guild? If searching for a person to trade with is too big based on the number of team owners within the game you could create a "Trading Block" for all to see that would list who you are offering and what you are looking for in return.

Also for those people who can't afford to purchase "In Game" items such as Gold Balls, Heal Kits (I know you can get them for free when you're in a guild but this way you could get more faster), Auction Coins (same as heal kits), "In Game" money, and even builders. It might increase your gamer activity if someone who can't afford to purchase items with "Real" money can still obtain them and get the benifit of having them.