You might like a cruise - I certainly wouldn't be put off by the fact that you don't like musicals or tribute acts! It's true that there is usually some entertainment of this sort, but it's easily avoided. Although most music acts round the ship often tend to be playing 'hits' with some sort of theme (country, latin, pop etc), but it's good enough background music while having a pre or post dinner drink. There's often other entertainment - on our last cruise there was a magician (better than its sounds!), a hypnotist, a duelling piano show, comedians, acrobats, trivia, language lessons, a talk about the Panama Canal (as that is where we were sailing) as well as the musicals and tribute acts.
I'd say go for one of the larger ships, with plenty of ports of call, you honestly won't have time to get cabin fever - and your six year old will have a blast, the kids clubs tend to be really great - a step above those in most hotels, in my experience. Royal Caribbean are great for kids, but other lines such as NCL (our favourite) and Princess will have loads to do as well.
If you are used to high-end all inclusives, then I'm not sure how a cruise will compare - I've done all inclusives, but more at the Rui level - and the drinks (branded rather than local) choices and food on a cruise beats those hands down - there is generally a good buffet, but you don't have to eat there if you don't want to - most cruise lines have their main dining rooms open at breakfast and evening, and many offer a choice of other places to eat at other times as well. Plus there will be speciality restaurants as well, although these often come at a supplement.
I do think with a cruise, it's usually a case of you get what you pay for - more expensive will generally be more luxurious, with better food and entertainment than the cheaper end of the market. But on the other hand, there may not be as much to do for the six year old on a very expensive line.