What benefits do alliances give you?

Allies sharing Starbase benefits is something that's voted upon. I believe you also get really cheep tech trading with alliances.

Your allies will also be inclined to support you when another race attacks you. I assume that this also might make opposing AIs less inclined to make war on you...

Allies share the benift of war bonding in this case when you go to war the ally will (eventually)... the starbase thing is voted upon in the UP votes it is random selection and you have no control over the vote being voted upon...

that benift the UP gives could be that starbases assist or do not assist allies with the same benift as you get from the base..

I assume that this also might make opposing AIs less inclined to make war on you...

Unfortunately not... Or not that I've noticed anyway. Still, it makes the resulting war a fair bit easier.

I assume that this also might make opposing AIs less inclined to make war on you... Unfortunately not... Or not that I've noticed anyway. Still, it makes the resulting war a fair bit easier.

your wrong
=P
if you read the patch notesi believe for 1.1 it says that AI will take into account Alliances when declairing war.
IE if you have the an Allie who is the super power and your military isnt the lowest you wont get attacked basicly.

If you have a strong military, most AIs won't trade high level military techs to you. If you ally with them first, they will.