SirPrimalform: I think if it's only one PM per person you can't call really it spam. After all, they are people who have previously played. Unless they've specifically said they don't want to play any more I don't think there's anything wrong with asking.
I think of it that they have reason to not play anymore otherwise they would sign up. It's not like all those mafia threads are hidden and they can't find them and decide themself. I have exaggerrated by calling it spam, though, and don't think someone should be too annoyed for getting such message.
We are cluttering this thread a lot. :-)