The MWR card IS NOT, as you say, "especially for the campground", but instead for the other MWR facilities on pass that receive very little use. Most MWR card holders that live in town, (3-15 miles away), wont be to eager to hook up their rigs to use the campground.
At the current time, Military and retired Military are given priority in the winter months. However when the campground is less than 40% occupied in the summer months, civilians are welcome. Regrettably, MWR is planning on giving civilians equal priority twelve months per year.
Incidentally, the MWR card is $20.00 per year, not $10.00 for three years.
At the current time if a civilian is found to occupy a site and a military person needs a site, the civilian will be required to move out. Hopefully your concerns will be brought to the command and higher ups in the MWR chain.