I have seen a huge, something like 30x50", print made from Ilford 3200. It was amazing. Yes, there is an advantage to MF. I have enlarged a 645 shot to about 36" wide, and it looked really good. Lots of lovely detail, yadda yadda.

Every camera has trade-offs. The 6x6 format is good, and Yashicas are good and light. I have a Yashica 635, and it produces good results. I have a Fuji 645, a Pentax 6x7, and a Pentax 645. All good cameras, each with something special. If you want a folder, you may want to consider the Fuji folders. These are excellent cameras. If you want an older folder, what Mr. Kreckel sells looks good.

You might also consider (gasp!) a Holga. You can use it, have a bit of fun, and you only spent a little bit of money on it. They can produce reasonably decent images, and you will never care if it gets dinged up. The only drawback to it is when you have to make a lot of snaps with it in a short while. I used one to cover the Occupy Seattle's first big event, and the film advance knob left my thumb and fingers red from the effort. But otherwise I take it when I know generally the light conditions, and the camera could get banged up easily.

My recommendation: set a small budget and stick to it. There's lots of fine choices for cheap.