I applied to 23. At the beginning of the admissions process I had no way to tell how schools would view my app. On the one hand I had a pretty low undergrad GPA. On the other hand, my post bac GPA is steller, as are my EC's, LORs and research experiences. I too am beginning to think it was overkill because depsite a handful of rejections so far, I've also been getting interviews across the board--low tier and high tier. And while I'm excited at the prospect of getting in somewhere, the process is very expensive and until I get a single acceptance I have to keep on scheduling interviews for EVERY school just to be safe. I'd hate to reject an interview only to find out that I didn't get in anywhere else.
So my answer to you, mashce, is unless it is difficult to judge where you stand competitively, I would apply to around 10-15, choosing ~3-5 low, middle, and high tier schools. I think that would cover you pretty well.
Good luck!