Years back at Fort Robinson State Park (3 miles west of me) we had a similar event called a, "Black Powder Camp" for the purpose of celebrating the Fort's 125th Anv.
It was a huge success which saw all groups of reenactments come together. No group felt left out, and the tourist loved it. So did the Cavalry that showed up in all their 1870's regalia. It was a good time!
Our Plainsmen Event would not cover such a wide era as to see cartidge firearms. That would be left to the later Plainsmen of the 1870' - '80's...
I think the eastern states could also benefit from such an event as well. Afterall, it was also the 1850's - 60's east of the Missouri as well, and I'm sure some extrodinary times in history took place back there, not including the Civil War, bit not leaving the Civil War out either.
I think the potential is here for such an event. We just need some starting places. I'm sure I could come up with one.