I love the idea of getting the guys together, but maybe let them decide what they want to bring as gifts. I think the possibilities for humor are endless: a flask for the diaper bag (for tough days, ha ha) or a Devo suit for diaper changes, Heavy Metal hits done in lullabye fashion.... If you are doing a man party, let the party be their's.
The only flaw I see in the idea (even though I love the idea about cloth diapers) is that *they* don't get to choose the present. I'd say, if they ask what you want, lead them to the registered diapers, and if not, let them choose what they like. Or, you know, run this idea by your husband. Chances are, he knows your friends better than we do, and could give you good feedback.