Here are my thoughts: Call up a hotel or two that you are thinking of, see what kind of advance timeframe you would need in order to block off 5 or 6 rooms (and the rates for that night), and then post up a drop-dead date. If we get more than a couple people to call and make reservations by that date, then game-on. If not, then we do a standard day cruise.
MNMazda thrives on indecisiveness. If the overnight is gonna happen, you're going to have to make the call and let people say "yay" or "nay".