dl-hoffman, (sorry, can't find underscore), I have an RP3, with the same upgrades as you have, and thought I could try a cartridge upgrade, but couldn't afford a whole MP200, so just went for the stylus, and it's terrific. The basic Nagaoka sound is still there, but there seems to more space around instruments, with more detail, too. The stylus/needle sits a couple of mm lower than the 110, so I raised the arm and it all seems OK. The cantilever is a tighter fit into the cartridge body, so presumably gives a better contact.
So, when you're looking for an upgrade, and money is tight, try it.