Here is a link to a few tunes I recorded with an ME50B a few years back. They are a little bit skewed because I recorded them into a POD amp model that the engineer wasn't too specific about (I hadn't quite got the full effects GAS so I wasn't that inquisitive). My clean tones all go directly to the POD and the others go ME50B > POD. There is a little wah, and a handful of the Muff model and the ODB-3 model, and some Slow Gear also. I'll let you judge for yourself how the tone is.
I would expect this to be a lateral move at best. There is a little bit more control of the ME50, but I wouldn't expect to get this great newfound tone over the Digitech. I would also expect the Me50B and 20B to sound very similar. I only tried the ME20 at a guitar center, but my initial impressions were, "this is like my 50b."
If you can get to a store with one in stock, plug into it and make sure that you are getting an upgrade.