When I got my 1st MF, I decided to get rid of all my 35mm gear, then went on a hike with my brand new Mamiya m645. Found muscles the next day that I didn't even know I had. How'd I find em, They all ached.
Thirty-five millimeter is just downright GREAT! Why should a person want to leave it UNLESS he finds that a larger camera would not change his chances of making an image he likes to make? Read on.
Whatever format does not impose upon your enthsiasm is the one to use. At an early time I realized that except for sports, all of my (allegedly) memorable images could have been made with Medium Format, but the fact was that the Leica M2 was with me everywhere while a MF camera could not have been. You cannot take pictures if the camera is at home.
Be lead by your enthusiasm to make the image. Don't be put down by format. Not many great photographs are technically perfect. Take pictures. Enjoy.
35mm is still the most flexible format out there, it seems. It is a great all-rounder, and so on. From your sentiment about using a 50mm lens and nothing else (which, by the way, I understand competely having shot more film through a 50mm than anything else over the years), you may not really need that flexibility that much. I would just really look into cost effectiveness of the move - how much can the sale of your 35mm equipment really earn for you? Also, I have come across nothing but regrets from people who sell of one format to get into another, even if the majority of their work happens with the "new" system. I would second what David wrote above - unless you can really make a financial difference of appreciable proportions by selling off, keep your old gear.