re: If only the rovers were nuclear powered
To be fair, I think there were weight and other tech issues for nuclear power on these particular designs that made it impractical. Design on these rovers was already a bitch because they were working on the same basic balloon landing system as the Pathfinder, and were already trying to stuff ten pounds of potatoes into a five pound bag. It's a miracle they got the rovers to fit on the landers.
Don't hold me to this, but I think that the MERs are pretty much the maximum you can land with the current bag system.