I had an MS60B and a B2 Four: the latter was better in almost every way imaginable except the real estate it took up on my board. I didn’t like the amp sims in the MS60B, though, so if you like the GK or Eden sims, maybe that’s a difference maker.Is it worth it to you if you already have the old 60B? I can't tell you that. It depends on how you use it and effects you need/want. But if you get the chance to try it (from a store with a nice return policy), I'd definitely give it a go.
Given how cheap the MS60B+ is new, I can’t really see the argument against upgrading. It’s not like an argument about upgrading your Pod Go with an HX Stomp, which would be a significant investment to make the switch.