Allies can be beneficial, but you really want to work on choosing them early on.
I recently finished a game on Tough with all races present as the Drath. I had chosen max diplomacy, the diplomatic party with diplomacy benefits, I was basically a diplomatic god. I ended up only having to destroy the Yor, Arceans, Korx, and Iconians. The Dregin were defeated by the Arceans, but I had allied with them. Everyone else was my ally.
First, the more allies you have, the worse off your enemies are, if for not other reason then when your allies are dragged into a war, they end up losing all trade with them.
The other thing is that it releives the burden of having to research as many weapon techs since you can aquire them via your allies.
As far as I know, the motions in the United Planets tend to go your way because your allies vote to benefit you. Also, if the motion regarding Starbases has been passed, you can get that benefit. It may not sound like much, but consider the mining starbases (I could be wrong on that).
Lastly, its always fun to be able to run proxy wars by having your ally attack someone and then to supply your ally with decent ships (ones with good engines and decent attack).
END COMMUNICATION