A newbie to RnD told me that it's bad that you can't restart the game without going to main menu. So I was thinking: Good idea! A simple button or something (how that would be solved for already existing levelsets with graphics, I don't know...) to restart the level (without pressing Esc to quit and then start again) would be a good idea.
Not a very important idea for experienced players, but a bit important for newbies who fail a couple of times on each level...
Personally I'm so used to hitting escape then enter (or F2) that it makes no difference to me. But you're right, I didn't know you could save and load for a long time. (not to mention snapping!)