You and I both know that there's a huge difference between Star Wars Land and a new 12-Loop steel Aquaman coaster at a Six Flags. SWL is going to be charming, creative, spectacular and unforgettable (unless, of course, something goes horribly wrong). I honestly don't think it's going to doom Disneyland any more than Space Mountain and Big Thunder did (if the web had existed in its present form at the time, we'd have seen concerns over Space Mountain, Big Thunder, Indiana Jones, Star Tours, New Fantasyland, Toontown, Haunted Mansion, Pirates, New Fantasyland, Splash Mountain ("It's a nearly off-the-shelf log ride based on a racially insensitive flop movie with reanimated corpses from America Sings!") etc.
Star Wars is now Disney, and Disneyland is going to keep changing to accommodate public tastes. It always has...since day one. To suggest that the park is dooming itself by building things people are going to like is... well, I'd say ludicrous, except I understand that you're talking about the ineffable. When you say "doomed" I think you're talking about the park losing its soul. I worry about that too, as I think Disney, as a company, already has lost it. It's still a massive mothership of creativity, but it's long since abandoned any altruistic goals it may have once had. The fans are what keep the "magic" alive, because they "get" it.
What many traditionalists ignore, though, is that for the new Disneyland fans, Star Wars IS magic. It gives them the same rush we once got from films like Peter Pan. DL's soul may be "doomed" for many of us (and I don't think it is just yet), but for the up-and-coming fans, it's going to be better than ever. Things change and adapt or they disappear. Disneyland, as it always has, is changing. It'll be more successful than ever, and I think the "mood" damage will be far less than, say, what happened when they destroyed one of the world's greatest audioanimatronic showpieces and replaced it with a C-ticket dark ride just so they could sell more plushies.