I have a number of Stan Lee sigs that are CGC'd on books that he didn't write, but those books are synonymous with his name. For example, I have a number of Copper & Modern Amazing Spider-Mans that he signed for me, because when you think Spider-Man, you think Stan Lee. I know I'm not the only one who thinks this. And it's true for me. Growing up in the 80s/90s, when I heard Stan Lee, I immediately thought Marvel and vice versa. So, maybe this is a generational thing?
As for some of the other Stan Lee signed books, I am guilty of getting a "non-Stan" book signed (using non-Stan in quotes since I still think Marvel and Stan are one in the same, please don't hate me). For example, I do have an Edge of Spider-Verse #2 signed by Stan. I did it because he helped create/write Gwen Stacy even though he had no hand in creating this particular version of that character, Spider-Gwen.
I know it may not make sense to others, but it does to me, and that's the whole point of collecting. You collect/get what you like.
Now as far as holding or selling, at this point, I'm a hold. I plan on holding for awhile as I'm not in a hurry to sell those books at this time, but if I need the cash, I may. Again, you should do what you want based on need. Other have pointed this out in this thread as well.