I have a few hundred shares of RCL and it is a hoop-jumping experience these days to get the OBC. I just sent my requests in for my December cruises on Liberty Of The Seas, but have not received a reply yet. In my case I do not have other OBCs but I did get the balcony cabin discount that is a C&A perk.
My view is, I will always ask for the OBC no matter what other discounts and credits I have. I'll leave it up to the cruise line to decide if I am eligible.