I have done the 3 and 4 night cruises on Carnival out of Long Beach and they are a hoot. But there is a big difference, the 3 night ones are genuine booze cruises with bachelor and bachelorette parties, makes for prime people watching. They run over the weekends. The 4 night one stopped for the day in Catalina which is a pretty nice day trip - and you still get to visit one of the Pacific's true dumps, Ensenada. Those left mid-week and you got a very different crowd. After last year Carnival upgraded to larger ships and sold off the previous two for scrap.
Royal has some very cheap fares which even if they hit you for a single supplement still aren't bad. I am in a similar demographic and enjoyed the 3 night trips completely. More craziness than usual, but so what?