Welcome to cruise-chat.
I think Carnival is the only cruise line which has it's own on-line community.
The Grandeur is an older ship but it is well maintained. We were aboard her this past summer and had a great cruise to New England and Canada. I don't know which ships you cruised on with Carnival, but the Grandeur is probably closest to the Fantasy-class when it comes to size and things to do aboard.
For the most part you will find RCI and Carnival to have more in common than they do differences. The crew on the Grandeur was outstanding last summer, and I was surprised at the dining room food. Not to say I was expecting it to be average, but it was just at a higher level than one normally expects with a mainstream cruise line. The crew was happy and it showed in the cruise product they offered.
RCI does have a lot of revenue centers, perhaps more than Carnival. However on the Grandeur these are not as prevalent as on the newer, larger ships.
We have lots of members with RCI experience here. If we can't answer your questions then nobody can, on any board.