What is it about the mailbox stores specifically you'd like to monitor? Have you looked at any of the following application templates?
Exchange 2010 Statistics with PowerShell
Exchange 2010 Database Availability Group
Exchange 2007-2010 Mailbox Send and Receive Statistics with PowerShell
Our UX team is also looking for feedback on some mockups they've created for some potential improvements to our Exchange monitoring if you are willing to participate and provide suggestions or comments.