I'd say you'd be doing the wrong thing! The BG500 is ok for a budget amp whereas a MB should be quality gear. (never owned a MB, but heard them a lot)
My BG is now my home practice amp, it was missing some low end and punch for the sound I was after. It's been fairly reliable for a chinese made amp, tho I have lost a couple of the small preset memory buttons which is a bit of a pain, but I can dial the sounds in pretty easy now, knowing the amp. The post DI out seemed to distort/overdrive the signal a bit on mine as well, but gave it a colour to the sound I didn't mind.
My advice would be don't downgrade... if your looking to change amps keep it with the better know/ proven models.