I think having an MCM is certainly worth it. I would call it the equivalent of the CCIE for network engineers. It marks Cisco people as the best of the best. They have to take a written and lab. Many people can pass the CCIE written, but then fail the lab.
Those that have the CCIE easily get premium salaries. $120,000+ is common.
I would estimate that the MCM for SQL Server would be similar. There are many people that can pass the SQL Server exams for MCTS and MCITP. The difference for the MCM is the additional Lab exam that is timed. This will remain a premium certification that only the best will achieve.
For SQL Server, these guys are likely already making premium DBA salaries in the top 10% of the range. So I don't know if the MCM will mean a raise. But it might help. Likely it can be used as a marketing tool for consulting firms. If they send a MCM to deal with a project, it could justify a higher billing rate.
From what I read, it will be impossible to be a "paper" MCM. If you see someone that has the MCM for SQL Server, you know you have the real thing.
Just my opinion.
I plan to finish upgrading my certifications to 2008, then I will focus on the MCM.