Well, just as a little personal experience thing here. Most of the problems we seem to have with the nominations (at least, this was the idea I got from the posts) is personal commitment for the mod(s)-to-be. But seeing your own screenname up there next to the word "Moderators" gives a little bit of an incentive to come on maybe just a little bit more than you normally would have.
But anyways.

I think maybe, as for the post numbers for old RPGs to keep/delete, there should be a system something like this: anything over 100 posts is automatically in the archive;anything from 50-100 posts is put up for discussion, either with those who were involved in the RPG, or if very few of the members are around any more, maybe in a large topic at some point; and anything less than fifty can be specially requested by someone (they don't have to be involved) to be archived, along with a reason as to why the RPG deserves it. Once everything's straightened out, mods can delete maybe two to five topics a day, so that the RPG forum isn't suddenly overnight down x-hundred topics.

Two weeks sounds more reasonable to me than a week. Maybe even longer, since sometimes people have to leave for extended periods of time.

But there probably should be some sort of incentive to keep RPGs going.

BTW, the RPGer rating topic sounds like a very good idea.