The advice on these threads can be confusing, because everyone's situation is different.
In some other fields, away rotations are essentially required. It's very difficult to get an Ortho, Derm, or ENT spot without away rotations. Not impossible, but most people have them.
In IM, they are not required at all. Most candidates do not have them, but some do. An away rotation can certainly get you noticed by a program, and if there's a very specific program you want then a good performance at that site may make the difference. Of course a poor performance will also make a difference, just not in the direction you are looking for. Whether a personalized PS explaining why you're interested in that program, along with the new signals we have, would essentially fill the same need is unclear -- but probably true.
So, if you're already a competitive candidate for those sites, unclear if an away will change anything as a signal + competitive candidate + PS explaining why you want to be there may simply get you an interview. If you're not a competitive candidate, then it's also unlikely to make any difference -- no matter how well you do there, if you don't meet their minimum criteria you won't get an interview. Where it might make the difference is in the grey zone between those two, and there's no way to know if you're in that grey zone.
Of course, perhaps an away rotation there is a chance to be closer to home and something you just want to do anyway. In that case, might as well regardless of the above.
All of this is for US MD candidates. For DO and IMG candidates, an away rotation may make all of the difference. Unfortunately, DO MSPE's are often less than helpful and it can be very difficult to assess performance, more so for IMG's. A local rotation with an excellent performance could have a huge impact. This assumes that the program takes DO/IMG's and that your exam scores fit their ranges.
So, clear as mud.
TL;DR version: If you want to do it and it won't be a huge financial imposition, go right ahead. If not, signal + personalized PS is probably about as good. And perhaps most importantly, one of my away rotations (years ago) told me where I did NOT want to be -- and that was very helpful.