An idea while i still remember it:
How about creating higher tier summons of the same type?
Like, if you put a tentacle egg into low quality cum, you'll just get a normal tentacle right?
But if you put the same tentacle egg into a high quality cum, an elite version will be born. (Maybe with skills and powers?)
I think this could be pretty cool, the player is also forced to choose between high quality cum preservation, or getting elite summons by sacrificing some of that high-tier cum since hatching eggs costs fuel.
Neat right?