Jacob, those flybys aren't "free". You have to expend manouvring fuel to make it work, and for a LOT of assists that's a LOT of fuel. [Just a guess here, but probably more than it's got]. The whole process would take years.

Even if you did finally acheive Saturn escape velocity, you'd only just do it and the trip to some other planet would then take decades, most likely. The chance of arriving safely and in working order somewhere else are slim indeed. (recall that Cassini runs off RTG's which have limited life, and you also used up all you in-system fuel reserve for the assists)

In short, if you want to visit Uranus or somewhere else, send a new mission!