tid242, I like those ideas except that you'll have to balance out the advantage of increasing the maximum allowable colonies versus giving commonwealths more benefit to their Owner Race - so that one helps one gamestyle, the other a different one.
I'd suggest making only one of those two a Tech Tree "journey". Certainly have research to allow you to expand the number of colonies allowable, forfeiting time researching other, less "lovable" tech like how to kill people with lasers etc. But also buff commonwealths with what they give from the Start. Make that "offering" improve as their Owner Race gets more powerful (whichever way, number of colonies, number of technologies known, number of allies etc ie conditions taken from the player's Victory Conditions as set up in the Galaxy Setup Screen, basically), as let's face it, you're less likely to say No to your Owner if he's holding a plasma bomb than holding a cute little laser gun. But maybe that way means you take a diplomatic hit with other races.
Essentially: Can you make "allow more colonies into your civilization" a more Benevolent/Pragmatic route, where as "Impress upon your Commonwealth to give you more good stuff by showing them how you could crush them" is more a Malevolent thing to do...
From what I've read on here, what people don't like about commonwealths - leaving aside those of us who like micromanaging 50+ colonies one-by-one - is that it doesn't give enough goodies in terms of bcs, alliances, resources etc - to the player who still owns them.