Note: Yes, I could say "It will feel pretty much like a November day" (e.g it resembles a November day) but this no longer sounds like I'm comparing it to previous days that perhaps felt 'less like' a November day than today does. Slightly different meaning :)
And if I said "it is much more like an opening act", again I am making a comparison, e.g "more like an opening act (than a closing act)".
In other words, "much more" is a comparison of difference.
"pretty much" is a comparison, but of what makes two things similar, not different.