My theory is a bit more complex than that-basically the Augirians have to expand their threat index in step with their tastiness, but the easiest way to do that is an alliance. But the most obvious ally of convenience is Hanse Davion, who is, let's admit, going to make the Capellans and Taurians hate you even more. So letting Hanse build bases and move his RCTs into the Coalition to jump off for their next conquest is not on the table. Even technology trade and ecconomic treaties are dangerous when the Taurians might wheel their Mechs away from the FedSuns border and clamp down hard on you if they suspect you're making common cause with their enemy.
Allying with the Capellans might seem more appealing at first brush, but they're the senior partner in any arrangment, and you can expect to be treated as a tributary. Offer up all your Mechs and submit to rule from Sian, it'll just make things simpler for everyone. The FWL can't find their rear with both their hands tied behind their back, so finding you guys for any treaty negotiations is fraught with peril.
The Canopians might supply you with Partisans until you're up to your eyeballs in AC-2s, but has that ever really helped anyone? And everyone else is too far away, though Comstar might give you a lot of money if you let them take some scans of the Argo and work out how that thing works...