It sounds like you're falling into the exception area I mentioned, Ruvy, in that you're finding real insufficiencies with your current Bronica. Many years ago, I sold my Bronica and bought a Hassy. The difference was that I had the first Bronica model, and at that time their lenses weren't very good. Modern Bronica lenses are far better.
Mirror slap, however, is part of the MF SLR beast, and difficult to get around if hand-holding the camera. A Hassy won't solve all of that problem, though. Along that line of thought, if spontaneity is a critical requirement, a rangefinder may be a better option. For me, that need is satisfied with a Leica M, because I don't feel the same need for the benefits of medium format for those types of images.