I think it depends how much you feel invested in the site. I certainly wouldn't volunteer in this way for just anything or anyone.
I started out as a regular member, and got so much help from the site (and enjoyed reading it so much) that when I was asked to help out as a moderator, I was very pleased to have the opportunity to give back. I spend enough time on MR anyway that it seemed like an enhancement of my forum experience.
I found I very much enjoyed the mod gig, and said yes when I was asked to be an admin a couple years later.
For me, this type of experience has proven to be directly relevant to my RL work (management team at a public institution). I also find that the cooperation among the mods and admins gives me a lot. I learn things, and enjoy both the more serious discussions as well as the banter and humor.
It never occurred to me to want to be paid. I was asked, I knew it was a volunteer gig, so I made a choice based on what I know.