After riding in some of Minnesota's trail systems, I have come to appreciate them greatly. It's almost to the point of "name the price and we'll pay it". Like Stumper said, we can safely ride our ATV to the trailhead, which would reduce congestion in the parking area. Perfect.
Even if the state collected a small $30 fee for a trail system sticker, which we would happily pay, that would add up to big revenue for the state. But there's no reason to take away plates from liscensed ATV's that have all the same requirements as cars need to be on the road. ATV's are safer than motorcycles, period.