IMO that is not a good idea (Many people have done it, some had no issues other had gotten into some), MS is a series of active libraries (Just like DLLs on Windows) that are use by most of the Application on Cydia (and Cydia itself), Those Libraries are update for a reason (bug fixes, some more critical than others, new features, performance issues). If any of the plugins and application try to call for any of those libraries that may have been updated with a new feature and it is not there, you can get into real nasty and system wide failure issues (you may also just get a error and that's it, it all depend).
I know that if you search and read, many people have Battery issues and downgrading MS "seen" to reduce this, however consider all those that DON"T post (because they don't have any issues) and all those (like me) that are running most current version of MS with no Effect on Battery.
Anyway that's my $.2