Make sure you let them know when you get there. I registered for my Romance Rewards and I even told the lady upon check in that we were repeaters. I never received any information on the dinner until I called and by that time, it was too late.
Officially I do not think you need to be a Romance Rewards customer - simply mark on the check in card that you are a repeater and you will get an invite. If for some reason you don't and I say this because we have been missed on the official paper invitation at least once - go to the dinner anyway.
If you don't receive an invitation just call or go to the guest services desk in the lobby, tell them you are repeaters and they will sign you up for the dinner. You really shouldn't just show up since they need to know how many people are attending. We always have a great time at the repeater's dinners!