I doubt the concierge can provide any real help getting MGM to move faster, all they do is ail the mailbox we do...I guess it couldn't possibly do any harm though.
Recent DP, MGM seems backed up. Emailed at 30 days after checkout, followed up 11 days later, received response from MGM 6 days after that(so 17 days after my initial email). Stay credit hasn't shown up just yet, but it has only been a couple days since MGM replied.