I think I need to clarify my question-
If you were to have a tour guide (from any of the popular companies- I know there are a bunch) which "sight" is best enjoyed with a personal guide to explain the history, background, etc. Despite all my obsessive reading about these beautiful places, am I going to walk away from the Pantheon for example & think "duh" I wish I had used a guide to help me understand more about it, the times, the people, etc. Another example, is Vatican city self-explanitory where I would think to myself, "okay we probably could have done that on our own & not spent that extra money for several hours with a guide when we could have enjoyed and interpreted that by ourselves?" My husband doesn't like guided anything, but he conceded to let me pick one particular "sight" that we could use a tour company.
P.S. Thanks Frank, for the question. I don't think I explained myself enough :)