Here's the match as I remember it,
Not all programs send rejections letters.
MSPE's for IMG's...well, that's variable. In the program I'm in, I had a converstaion with one of the associate PD's the other day who was going through applications...she didn't know exactly what to do with IMG applciations. The most important thing she felt was to assess the medical school itself. How does she find out if the school is good or not?
Judging by the conversation we had (yes, this is my opinion) it seems that in terms of the MSPE, I wouldn't weigh too much on it unless it said something really BAD. Perhaps, something REALLY GOOD may give a plus point.
Overall, when it comes to IMG's, USMLE scores and LoR's from US MD's at recognized teaching institutions would count a lot more than MSPE's.
hope that helps. But please note, this is based on a convo I had with someone who was trying to the grapple with the same question you have...just that she's on the other side of the table.
GL