It depends on a person. For me the lectures deserve all the praise they've got and more.

I've read Feynman lectures twice. First time in the secondary school -- it was above my head but it gave me an understanding, the right models to work with later. The second time I read it in the university after I'd already studied the topics by other means (through complex math using e.g., Landau and Lifshitz textbooks). Now, I could appropriate the full depth of the lectures.

It is often useful to have several perspectives on a subject , to know it better in particular to solve complex problems (the more tools you can apply, the better).