the other day, Captain America played by Chris Evans is a far different character than the one Jack Kirby was drawing in the 1960s, who was already a far different character than the one Joe Simon created in the 1940s. Then you throw in Ultimate Captain America and Cap-Wolf and (the original) Nomad and the Heroes Reborn Captain America and the over-armored/over-pouched 1990s Cap and Captain America For President and the Captain America Hotline and Reb Brown and Captain America: The Musical and... (Am I showing off enough geek cred here?) At this point, the character of Captain America represents so many different things that the character, as a whole, is essentially meaningless.
Same thing goes for Superman, Wonder Woman, Spider-Man, Dick Tracy, the Phantom... These guys have all been around so long and re-written in so many different ways that they're primarily just ciphers for whatever any given writer wants to do with them. So, the question is: do they retain any literary value they may have once had?
I say yes. But just not in the aggregate.
Batman's a good example. Frank Miller's The Dark Knight remains one of the seminal Batman stories. Indeed, it's not hard to argue it's importance in the history of American comic books. But that's clearly a very different Batman presented there than what Bill Finger and Bob Kane created. It's a very different Batman that what Denny O'Neil and Neal Adams produced. It's a very different Batman than the one portrayed by Adam West. The gestalt Batman -- the Batman you might come up with if you mashed all the different interpretations together -- would be pretty banal, as many of the individual bits that stand out on one end of the spectrum would be canceled out by the stand-out bits from the other end.
But The Dark Knight remains a story with significant literary value. Precisely because it's an interpretation of Batman that was very well done. It does NOT match the Batmen that came before, or the Batmen that came after. But it's a valuable interpretation. And, therefore, a valuable character of literary merit.
Regardless of what happens to your favorite characters -- if they're sanitized for big budget movies or "reinterpreted" or "rebooted" or whatever -- that doesn't diminish the great works that came before. Regardless of how many Watchmen prequels we get or their relative quality, that doesn't detract from what Alan Moore and Dave Gibbons did originally. The overall brand might get diluted, but the best material does not.