I have both the 200 and the 500. I would opt for the 500... Mostly for the variable contour. They show up in the classifieds here in the under 4 bills range pretty often. It will fit in the pocket of my Protec gig bags...
I love the 200 as well. Mine is buried into a combo cab I had built for acoustic support gig's- i don't ever need the contour there... They're both great amps. The MB500 is going to feel more like your Eden if you use the WT's Enhance though. The DI's on each are clean and quiet.
I sold off my last WT head. Miss that tone, though not the size and weight. Eden and GK are my two fave sounds when it comes to solid state amps.
I don't care too much about contour or luxuries like that for a spare head. For me, it's having suitable power to get through a gig.
The small size of a micro head seems very appealing for a spare.