It seems like this question gets asked a lot. What do the residents at your school say? I'm telling my students the same advice I got--too many aways and you look desperate. Do what you need to do to make your program happy then rotate at a program that you're interested in. You don't have to rotate to match at a great program; however, with that said, there are programs that heavily favor rotators. If you choose to rotate at the latter, I would make sure you are not wasting a month and consider your competitiveness before going there. I think the true value of an away is to see another program so you have a better idea of what you want when you are trying to choose between programs in March.
As for fourth year electives, I don't think they matter too much and I wouldn't kill yourself. Have fun. Do some private plastic surgery if you can--it's a lot of fun and you'll never see anything quite as nice again as an ortho res at a university program.
I did a MICU rotation and think it was a waste of time. Next July you'll be so busy changing lines and writing for TPN as intern that any fourth year experience won't matter after about two days. I also did a month of rheum. It was easy and I got to work on my physical exam, but man, you'll pay the price when you're taking a history for an hour and trying to sort out a rash with intermittent fevers. Just wait until you get pimped on the serologies. Good luck. Down with the big ten!