The problem with that is there's no way to win the game without expanding.  Even the science victory requires lots of planets producing research (And I won my last influence victory by invading everyone)

I think that the Minor Races should simply be made more unique. Give each one a unique tech tree with improvements and ship parts and other things, some of which could be traded away. The catch to that being that the race has to stay in the game long enough to research those unique things. So a player would have to end up deciding who to befriend and defend in order to gain those benefits and who to leave to the dangers of the galaxy.

Even more interesting would be to have lots of these new, truly unique Minor Races modded into the game as well because the more races there are to possibly be selected for a game the more random that game becomes since you don't know who you will encounter for sure.

Just my two cents on the topic.

I try to imagine this from the point of a minor race. How would we interact with a huge, scary, inter-stellar, tech savy alien race? Probably skeptically at first! Any deal that is not a response to an outright threat would have to come with some guarantees. Don't kill us, don't let anyone else kill us! If that's the deal, then paying tribute is definitively worth it, most likely by promising exclusive trading deals. Also sharing tech would be a worthwhile price to pay, as well as only letting our population go visit your faction on holidays. However, if you can't give us any help, we'll start courting someone else and keep you on an arms length. If you're willing to actively help us, joining your faction as a vassal to survive in a hostile universe in which we can't hope to survive on our own sounds like a good idea.

a) Signing non-aggression pacts should give you a bonus

Signing alliance deals should give a bonus

c) Getting influence over them should give a bonus

d) Establishing a trade route should give a bonus

e) The bonuses should be worth a war to protect. Not at all costs, but it should be a worthwhile factor.

f) Good bonuses could be anything from promising to support you on the next UP, add a unique bonus to your faction (not just a flat % bonus on something), unique techs that you lease (only available while in alliance), ideology points or events concerning how you treat your minor factions, etc.

Why has minor races ever been worth anything to a major race in any sci-fi show? Because they give increased diplomatic standings and available pressure. Because it's handy to have a few tech-wizards on your warships to keep some special deflective shield thing working. Because having access to a psychic when you want to do some black-ops is beyond useful. Something that twists the "usual" in a good way. In the spirit of GC - let it all be balanced out by its OP'ness.

I agree minor races are currently boring, and would love to see them made special and interesting. I made a post with some suggestions concerning money, one of my suggestions was the ability to outsource projects to 3rd parties and to buy unique ships and such from minor races using a new market tab.