I've seen great use of light-up bracelets in concerts, but three key differences are:
- The bracelets at concerts aren't advertised as something you're supposed to look at per se, which is the opposite of how Disney has marketed MB+
- The LEDs on concert bracelets are really bright (especially because they're often encased in some sort of diffusing material), whereas these bands barely seem to even cast a light on the owner's wrist
- The reason you can see them in concerts and they make such a good impression is there's a portion of the audience that is typically facing you or askew from you so you can see everyone with the bracelets en masse.
Thinking it through more, I think this does mean this could be pretty cool to see in Fantasmic! since you can at least see folks across the river, but that hinges on wide MB+ adoption.
Also I agree; had I not gotten the plain black MB+ during a sale on shopDisney, the only one I'd consider getting is maybe the gold and black Disneyland D band. The other ones are not great (and the first visit band in particular is really odd design for a band meant to be reused for future visits).