Absolutely. The sharpest lens you have is a Tiltall. While that Mamiya can be used handleld, a tripod will imrove the images from any camera.I had a C33 on loan during my buddies senior trip to SE Asia during the late 60's. Shot lots of film, loved the camera. I was a MUCH better photographer with it than any cameras since. I think the weight is not so much a problem as an asset, as is the view finder. Does a great job of forcing you to think about what you're doing. and with me, it really helped with the stability issues.
One other thing that folks don't put much conversation into about tlr's vs slr's. When you pull the trigger on a Cxxx, the shutter goes off. It goes off Now. None of that mirror madness slap, bounce, wait a while, then fire a spring loaded curtain followed by another curtain, fully expecting the camera to stay still. (oh,,, I love my Nikon F, but I'm good for an extra stop of shutter speed if not two stops with a leaf shutter).
And for sports, like horse shows. Trying to get the legs in the correct position with an slr takes a bit of practice and skill at leading the shutter release. And, I half way think people can respond to the slr noise and blink before the shutter fires.
Oh,,, and available light. My definition of available light is all I can carry ;-) Really puts the focal plane at a disadvantage trying to balance fill in natural settings.
I may end up with another C33 or C330 with three lenses. Only real trouble, a roll of 120 costs me about $20. Buy film, ship to North Coast, process, scan, ship back. So I really think my primary camera is going to be one of those dark side things that will use several of my existing lenses, with the 4x5 and hopefully a Mamiya kit as "I'm going to go take pictures and have fun today" equipment.
Having fought the battle in the early 70's with my Ftn, I think, if you go back to your smaller format camera, some good slow film and really lock the sucker down on a tripod you'll find the 35mm format will do an order of magnitude better that you've come to expect. I'm one of those guys that never gets rid of things,,, the Ftn will always be around, but it did teach me a lot about stability. But a tripod and asa 25 or 50 is a bit the PITA, when you can shoot 125 or 400 hand held. (ok,,, sort of hand held, Nothing really convenient about a C33 hanging off a pistol grip ;-)
You'll have a ball with the Mamiya.