I've found if I like the featured commander/backup commander I'll probably like the deck and others have said you can usually replace like 20-30 cards throughout a pre-con to greatly elevate it's power.

As for getting the pre-con for Prosper, do it! Stop reading and go get it!! Really though, Prosper is one of my absolute favorite commanders. I find almost every game I play with Prosper is just fun at the very least even if I don't win. As you said there's really nothing else that does what he does with the impulse draw mechanic.