They shoot very differently, IMHO. If you like shooting with the Mamiya 7, you may not easily replace the experience with even the wonderful Hasselblads. I'm afraid that the prices of the Mamiya 7 have been increasing so rapidly that if I don't buy one soon, I'll never be able to afford one. I'm okay with that, but if you think you'll want to use it in the future, I'd personally hang onto it. There aren't too many alternatives in that format, and other 120 format cameras have very different shooting approaches. Mamiya RB/RZ 67s, Pentax 6x7s, etc. are all very different animals. I think that's why younger shooters have been "discovering" the 7 so frequently of late. As recently as a couple of years ago, you could find them in the $500-$1,000 range. I'd guess prices have more than doubled.
Personally, I've regretted selling gear much more often than I've regretted buying stuff.
Just my opinion, take with as much sodium chloride as needed!
Andy