We did that on Costa also. I wore a royal purple satin robe trimmed with fur over my bedsheet and I carried a scepter. I stood out from the crowd. It was fun, but that was then. FWIW, I actually thought Costa was a much better product than the Princess cruise I took the same year. This was not quite 20 years ago.
Yes, I do think it wouldn't hurt Oceania to invigorate and energize their activities a bit. While they're at it they need to work on their menus throughout the fleet. But the food is still good, or at least has been on my 3 cruises in the last 12 months or so.