Minnesota Territory in Postmarks, Letters and History by Floyd Risvold catalogs the territorial period in great depth. Minnesota covers are not in strong demand. There are a few counties where there is some interest, primarily those in and around the larger cities. Most material goes begging. With an accessible territorial period, scads of interesting material, a large population, there would appear to be more potential than has been shown to date.
Demand is still weak.
A few new collectors seem to be off to a modest start. However, my record at projecting increase in demand for formerly moribund states is unblemished. Every time I think I see some upward movement, my next list produces abysmal results. The small up tick in demand noted last year noe seems to be non existent. Minnesota remains one of the worst states.