So, more Treasure Planet, less Yellow Submarine?I agree with DEFCON1. They want a Spelljammer game, they want a Jack Kirby pirate fantasy adventure. Too weird might mean 'too mechanically weird' or too many house rules. All this can be hashed out in Session 0. You are already reaching out to try and get more definitive answers from the players and consulting the Council of Eric Noah's Grandma here. It may take your group a bit to articulate 'weird'. The best bet is to give them examples of media that would exemplify what you consider a Spelljammer campaign and let them riff off that.