I am a marsh member, the other benefit that wasn't mentioned is some times people put stuff up for sale to only other marsh members, like when its an awesome deal they might put it up for marsh members first before going to the regular sale forum.
You don't have to be a member to go to the swaps, collecting trips, or the meetings. But if you are not a member then you will not get your food for free at the collecting trips.
The discounts are nice, and there is rumor that they are going to try and get some online sponsors that would also give a discount to members. Have to see how that goes though.