Some VERY good points, Geo. But I know (I think) you like multi-player games a lot
. For THAT dimension.
I would add (or disagree with) some points (humbly):
If I were your ally and I were weaker than you AND the game was a "one victor" game, I think you'd be better off sharing your tech with me and letting me do my best to help you to a final victory. You see, when I'm in a game where it's Last man standing and I can see that I am the weakest in the alliance, my goal is to help the others win. And, I think, they have a better chance of winning WITH my "pathetic" help than having to spend "energy" and time taking me out just to get my planets or colonies. After all, if I have the same tech, I can build the same ships as you and help defend warp points that you attack through, or spend time on producing minerals (etc.) and gifting them to you, or getting that opener you can't spend the EB time on while you are on the offensive. In fact there are MANY things a weak ally can do to help. In my opinion, though weak, I'm more useful as a weak ally than the time it takes to remove me. I could be wrong (and naive) as I rarely spend time thinking about "removing" a weak ally.
Though I may be in an alliance where I have no chance of of being the Last man standing, I gain my extra game satisfaction by helping my alliance as best as I can to "their" victory. In games like that, I would hope and expect my allies to understand this and understand it's better in the long run to "keep" me than spend the time to "throw" me away.
I do the same for any ally I have a partnership with. And I like knowing (hoping) that any partner I have knows this about me and trusts me implicitely.