Has anyone taken any tours of the above mentioned sites? Were they worthwhile?
I didn't take tours, and I wouldn't recommend that you do.
I especially think the truly enchanting opportunity about walking the walls is to do it first thing in the morning when they open, before the crowds arrive. That's what I did, and it was the highlight of my time in Dubrovnik. It's not so important to know what you're seeing as it is to just enjoy looking over the city and surroundings.
Perhaps there's a walking tour of the old town that's worthwhile, but I think it's a very easy place to see on your own with a guidebook. And again, it can get very crowded depending on when you're there, so being on a tour will mean spending a lot of time being herded from one place to another for a quick stop and look.
My advice is to see Dubrovnik at your own pace without an organized tour.
We did not take walking tours, but the walls is more about scenery than anything else. Regarding Old Town Dubrovnik, I would only consider the tour if you are a history buff and want more detail than what you can find in Rick's guidebook.