Everyone always stresses about how big you can print a 35mm negative forgetting that you don't have your nose up to a 16 x 20 print.
I just printed a show with 35 negatives scanned on a (gasp!) Epson 4990 flatbed and the prints were 17 x 22 and of all the comments I heard from my artist and graphic designer friends, most of them were what printer did you use, these look amazing.
Yes, medium format will look sharper and provide a richer tonality, but depending on your subject matter, this might not be much of a factor. For hand held street photos probably not, for landscapes, maybe yes.
I sold my Mamiya 6 to get the money to buy an M4P because the Mamiya was a little too bulky and slow to use for quick street grabs. When I look at some of the landscape photos I took with it, I get a bit sad but when I look at all the street photos I've taken since, I get happy.
Sounds like all your bases are all ready covered and you're just looking for something new to play with, so go with what makes you happy.