I've thought about upgrades to the tower and well, but I'm not seing clearly what they would add, and the problem is that building is an atomic operation in the game.
I also have an idea on the shelf about major projects, covering 4 squares, that would require at least 4 people to work together. Something like a church, for example.
But yes, another action is probably too much. An upgrade to the tower sounds like the right answer, and then everyone can just check there.