I've encountered the same kind of situation you described in my Seleucud campaign. They won't consider it in attacking you, neither out of honour or out of self preservation.
The exchange of map information and so on is fine, though quite simple, but the alliances, which should be most interesting to the direction of a campaign - of the diplomatic possibilities - but unfortunately an Alliance means absolutely nothing to the AI. I very much agree and have complained about the same thing on this board.
