Everyone has pretty much covered the current status of MARS correctly.
In answer to your question on benefits, we are authorized access to Class C Morale Welfare and Recreation facilities. With my MARS identification I've regularly in the last year used the Luke AFB recreation facility in Flagstaff Arizona. To learn more about the facility visit www.lukeevents.com
and follow the links for Fort Tuthill rec. site. They have some awesome cheap cabins.
We can use any rec. facility that is classified as "off post" and where authorization is classified as "DoD Civilian". You can find the sites in military travel guide books online. I'm currently looking forward to using the Fourth Cliff (Hanscom AFB) site in Massachusetts for a summer on the beach. So I think this is a pretty awesome benefit for us as volunteers and I'm very grateful that we are provided this by DoD Instruction.
I am the State Director for Arizona USAF MARS (AFF9AZ). You can find our new site online.