Impractical missions of the far future

Am I right that Uranus is a uniquely poor target for a Cassini / Galileo class satellite-tour mission, since it lacks a gigantic satellite for Oberth-effect maneouvres, so you'd have to carry fuel enough for every orbit change you'd want to do?

http://www.alcyone.com/software/botec/

suggests that it's 3km/sec delta-v from Oberon to Miranda, which is really a very large burn if you have to do it without benefit of slingshot. And I suspect slingshotting round Uranus requires a perigee low enough that you worry about running into the rings; whilst the main rings are well-delimited, http://wisp.physics.wisc.edu/astro104/lecture25/F16_10.jpg (a back-lit image) suggests that there are ringlets everywhere, it's no safer than trying to fly through the Cassini division.

Tom, contemplating icy moons.