I agree with your last statement, but I do find it a little funny that when I ask people to explain the appeal of Man-Thing, almost every single person essentially answered by saying there is no appeal to the character. Only MWGallagher actually seems to like Man-Thing as a character; everyone else just likes Steve Gerber and apparently puts up with Man-Thing as a necessary evil to get to read those stories. Except, of course, he's not actually necessary except on the meta level that his series exists as a conduit for comic book stories to be published. And that's a bit too meta for me.
I have to reject the notion that characters don't matter. Good characters do matter. Instead of being passive MacGuffins, some characters actually are story engines - the stories come from exploring the character. One of the reasons there have been so many different takes on Batman is because the character is interesting enough that fans and writers want to keep exploring the character in different ways.
It's interesting to note that Swamp Thing and Man-Thing came out at about the same time and originally had very similar origins. Yet the differences in Swamp Thing were interesting enough to trigger new ideas by new creators in response. If I had asked people to explain the appeal of Swamp Thing, I suspect there would have been plenty of supporters happy to state why they think Swamp Thing is so great. Yet nobody really seems to be invested in Man-Thing at all. Trying to understand the reasons for this is something I find interesting.