I'd say a periodic job that looks at the last update of all your blogs, and removes those that haven't updated in over a year would be generally agreeable.

If you want to be exceptionally kind, you can also email the submitter and tell them their blog has been removed due to inactivity, so they'll remember to submit if they start blogging again.

I suppose my dream would be that the protocolization of this from back in the day gets revived in some way. Like a google pagecrawl style index built up from blogrolls (though I don't know if the blogroll itself was ever literally protocol-ized), combined with some checking of RSS feeds for activity. Or webrings, or something else.

Though in some respects these are less smart than what you're already doing, but I would like to think there's an elegant way to make an index emerge organically to minimize the editorial burden of any one person.