When people is anyway paying $1500-$2000 per person for the hotel, I doubt $100-$200 for registration would make a difference, to be honest I don't even take registration fees into consideration when deciding if I would go to a show or not.
A worthy promotion could be including free registration to people staying at the show hotel
I skipped xbiz myself since it is in the month of july and probably a lot of people would head on vacation just after and I got 2 shows to go to in august.