"All periods have significant history. The question is, does a period (small window) have enough interest for the general public, to justify reenactments."
Absolutely. The 1840 to '65 period was active from Minnesota (Sioux) to the Southwest (Apaches), throughout much of California, the war with Mexico, Texas Rangers and Comanches, the gold rushes from California to Colorado to Montana, early buffalo hunting in Eastern Kansas, Indian conflict on the plains (the Gratten Massacre, Bluewater) Border Ruffians, Cracker Cowboys, and etc. All of these would hold interest for the general public, and allow for expanding the public's knowledge outside of the current rendezvous/cowboy eras.
Just a couple of current historical sites that include annual encampments would be Bent's Old Fort (1846) in Colorado, and Fort Union (1851) in North Dakota. All it takes is a group of like-minded men and women who want to explore a new time frame. The inclusion of percussion revolvers and certain breech-loading rifles doesn't hurt, either.