I live in Orange, and as a Disneyland regular, I just wanted to note that, essentially, the only rides that are really closed are the Matterhorn and the Monorail. The Matterhorn is almost 50 years old, and it basically goes down every year for some TLC and track work. I went on Space Mountain last summer at Disney World, and I would cringe if the Matterhorn got to that state.
The Monorail has essentially been operating daily since its expansion to the Disneyland Hotel in the 60's (And for moments where the trains were upgraded), and the station was starting to feel seedy. The result is going to be a brand new monorail station, completely new trains, and a new E-ticket ride in the Sub lagoon as a part of it. I doubt either of these attractions will be going down again for a long time.
The Haunted Mansion was closed for about three weeks for the Nightmare layover while the park was basically dead on weekdays (And the 2 hour lines winding down ROA and looted Nightmare Before Christmas stores seem to justify its work). IASW closed 2 weeks ago for its holiday layover, and it reopens this Friday. It's well worth it to me - the 2 hour line for Small World at Christmas also seems like justification.
I agree that the refurbs around 2003-2004 were excessive, when at one point, the Matterhorn (Annual refurb), Thunder (The accident), and Space (Overhaul) were all down at the same time, but this was after a long period of neglect by Pressler and Harriss. I'm sure MK will receive this sort of treatment soon if the management gets their heads together, and the payoff is well worth it. The seedy feeling that Disneyland had a few years ago is completely gone, and all of my casual-visitor friends who I have gone with in the past year have been blown away at how much better everything is.
Basically, as someone who has visited Disneyland every month for the past 6 or 7 years (When I lived in Norcal), and as someone who now goes every other week (I'm in college), I think the rehabs are very reasonable, and completely unnoticeable. THey payoff definitely outweighs the occasional missed experiences.
Thanks for reading a CA native's rant!