I had a few days in Rabat between Christmas and New Year, I enjoyed it, but it is quite a sanitised experience compared to Marrakech. There isn't an enormous amount to visit but it's pleasant enough to wander around for a day or two. I burned some points at the Conrad which was a lovely hotel in a very inconvenient location. If you want to dine next to the Crown Prince, it's the place to go.

If you can't do Marrakech, I'd rate Tangier, Fez and Meknes worth of your time over Rabat TBH.