The issue is that I feel as though you give something up either way - do an away at a solid but non-top 10 program can help in showing interest, but doing an away at a top 10 can help get an interview you wouldn't otherwise assuming you impress someone. Why is everything associated with medicine so anxiety-provoking?
I did an away where I liked the program for nuts and bolts reasons (reputation, geography, retina dept), but wasn't sure how I'd "fit in". Also I wanted the opportunity for the program to get know me, since no one from my school ever matched there, and they "take people they know". This was definitely a "reach" program for me.
My away was almost 100% in the residency run clinic, with little interaction with attendings. But...I got along very well with the residents, and tried to make the attending interactions count. I didn't ask for a letter (didn't know any attendings well enough), but told the residents it was my top choice, (by the end I knew it would be), and wound up matching there.
Only caveat is that I am a better candidate in person than on paper or in a 15-minute interview. There are smarter, more-published students from better schools than me. Yet I am a friendly, non-gunning, hardworking person that works well with people, patients and colleagues. It's hard to relay that on an application.
I say this not to be self-congratulatory, but simply to point out that you should know your strengths. If your application is stellar and you interview well, a month-long elective somewhere may hurt, since one innocent faux pas can sink you.
For me, it was my only shot at this program, so I had nothing to lose.