I really don't see any need for that. Most of the low-activity admins aren't the ones causing trouble, just a few of them. My point is that we should not be that concerned about lopping off problematic admins; we're not running short on them by any means.
The practical question here is how we go about determining which admins are "problematic".
You are approaching the problem the wrong way. You only need to determine which _actions_ are problematic. Wikipedia has a number of policies for doing that. Then you only need to act on it.
-- mvh Björn