Wendy I also think the quality of the tours varies with the different destinations and the local tour company the cruise lines use for the tours. Some areas of the world simply do not have quality local tour companies and I am sure all the cruise lines seek out the best they can find. South America (particularly the area you were just touring) does not come to mind as one of the areas that has exceptionally good tour operators.
My worst tour EVER was on Silversea in South America in the same area you were just crusing. Cannot remember the name of the port right now (similiar to San Francisco) but we drove for one hour to see a bicyle museum (terrible) and a tree that had been hit by lightning. We went round and round the block trying to see this tree we were all so bored. They then took us to a hotel that looked German to have a drink and use the restrooms and then it was an hour back in the bus again. Torture and I think we paid about $89 for that.
I know on the Baltic's cruise in August everyone was very happy with the tours and Alaska has had great reports too. The tours in Asia were generally good, the trip to Hanoi is torture but there is no way around that it is a long way.
Some love the free excursions, just the whole idea of not having to get the bill and having things included. Others feel that they do not want to pay for something they do not necessarily want to utilize. Like the dress code of the Formal or Elegant Casual some love the new dress code others feel it is totally unacceptable.
They do have a sampling on most cruises of reduced rate excursions that are either more limited in the number of people on the tour or that go further afield to more interesting places.
I guess it all boils down to the fact that we are all different and perceive the same situation in a totally different way.
The good thing is that there are nice options out there with multiple luxury cruise lines and everyone can make their choice according to their preferences.