It does not make sense sometimes that your allies wont help in a battle because their allies are attacking you.
Actually I find that makes it interesting and helps add to the name of the game.
"Oh yeah, we're best friends being allies and all"
"What? Help you? Actually... we like the other empire better and were planning on stabbing you in the back anyway, so..."
The diplomacy tree as is can add some good depth to the game. For instance I'll leave cease fire aggreements on the table just in case that empire gets the better of me. Start losing, accept, build better fleet, break cease fire, and wipe out what used to be a superior fleet.
Also can use it offensively, accept cease fire with enemy with a large fleet that could be trouble, ask them to defend your most heavily defended planet, and then with your fleet there too and phase jump inhibitors up, break the cease fire and watch the pretty fireworks.
As for giving out missions, could be interesting to have that around for manipulating enemies and "allies" lol.