I'd say it depends on which other wars would be going on and with whom the Thalans are siding at that point.
If the Thalan coalition is too strong, we could at least help the minor races by feeding them military techs (and get some bc or tech out of that).
If we can stage it so that other races gang up on the Thalans, let's join. Not only from a moral point of view, but also to avoid that the Thalans get their hands on any additional economic / manufacturing / technological capitals!
I wouldn't go as far as bribing other races to go to war, as that doesn't fit our profile. However we might consider it if the Thalans declare war. Sort of "let's pour some funds into helping the minors, trying to convince other races to join the defensive side"
I like that you're setting your standards high Tolmekian and for sure it would help to make the game more interesting. In the past I too often went down a peaceful route in Gal Civ II, making for rather boring games 