I think doing away rotations are a great idea. I did 3 sub-Is my 4th year of med school. Two were awesome, and one was a really bad experience. I received interview offers at the two places I had great experiences at and would be elated to match to either place, and did not receive an interview offer from the less than desirable experience (only applied because they said an interview was basically guaranteed if you did an away there; I would have certainly ranked it last if at all).
That being said, my point is that away rotations - for better or worse - give you great insight into the program, but also give you an opportunity to say "hey, I'm interested in this city" even when applying to other programs in that same city where you didn't rotate (you can always tell the PD that you wanted to do an away rotation there, but it was filled up or didn't fit with your schedule, which is likely to be the truth for most - scheduling aways is a nightmare). And if you do end up having a negative experience at a place, at least you know that it probably isn't where you want to do your residency and hopefully you ended up learning some things or experiencing a cool city. If you have a good experience, try to get a letter ASAP from someone you worked with closely throughout the rotation.
One thing you can also do is go onto the apgo.org website and search the residency directory for the programs you are interested in.
https://www.apgo.org/students/residency-directory/search-residency-directory/
Though these aren't always up to date, there is a section at the bottom that shows how many of their current residents did a 4th year rotation at their institution. Some have zeros all throughout - that's probably a place where it might not be too beneficial. Some have 1 or 2 each year - that could be a good place to check out.
Hope this helps and good luck navigating VSAS (I highly recommend getting titers of everything done now (HepB, MMR, Varicella), seeing what you're not immune to anymore, getting re-vaccinated, getting a 2 step PPD, flu shot if you havent done it yet, and making sure your BLS is up to date and still active throughout the end of fall).
