some of my best bock recipes use a blend of Munich I and Munich II for the majority of the grist (if not the entirety). I usually add at least 10-20% pils for the enzymes. I also like a touch of cara munich as well.
What is the difference between Munich I and Munich II? Is it just length of kilning (color)? I've chewed on both and didn't taste an appreciable difference.
Is the blend just for complexity (i.e. layering crystal malts)?
I agree that chewing on them, its hard to taste much difference - hell, its hard to taste a difference between vienna and Munich I. Munich II is considerably darker lovibond, so yes, its kilned longer. Most brands Munich I is between 4-8L while Munich II rangers from 8 to as high as 20 in some cases. I stick with Best or Weyermann whose Munich malts are on the lower end of the ranges.
IMO, Munich II is richer and tends to lend some more dark fruit malt flavor over the toastier type flavors from Munich I.
A lot of people make dunkels with 100% Munich II, FWIW.
Blending them, which I do a lot personally, especially in amber lagers, kind of gives you a best of both worlds flavor.