From my multiple experiences with the application process, this is my general observation:
-It is NOT about the number of applications, but it is about the quality. So read the program's application requirements carefully. If you meet their requirements, then apply, but if you do not, then it is just a waste of money.
-The process is COMPLETELY subjective....If a PD does not like FMGs, he /she will not interview or rank a FMG. So look at the resident roster before you apply.
-A poor application is a poor application. Applying to extra programs will not significantly increase the chances of interviews. When there is a poor application, the effort must be directed at making that poor application stronger, and not waste time and money with applying to more programs.
-For the most part, there is no such thing as "it is too late", or "all our interview slots are already filled". And I do not believe in the myth that if you apply on Sept 16, then you will have a better shot at getting an interview. I think this is non-sence, for the most part. In this game, the PD is the PIMP KING. He/she calls the shots. If the PD wants you, he/she WILL find a way to get you, no matter how early or late you apply (as long as you are within the application time-frame that the program stated). It is funny how interviews "just pop-up" when the PD is interested in the applicant. It is all very subjective.
Good Luck