Def give medium format a go. Even if it isn't for you, you can sell everything again for what you bought it for if you go for second hand gear.
The jump in quality was the reason I bought my RB67 but I've found that it has other benefits too. Having the camera on the tripod with the groundglass to look at while composing makes me interpret what I see and an image better than squinting through a small viewfinder. I feel a waist level finder and nicer to work with too.
Donít sell your 35mm stuff. With cameras itís all about the right too for the job and my RB67 really isnít the right tool for quick spontaneous shooting. I really really want a hassy H1 for thatÖ. If only I had the £ís!