I don't agree with alot of people's estimates of time needed for Disneyland...ESPECIALLY for first time visitors to the complex and who are avid Disney Theme Park fans. We spent 5 days/6 nights at the Disneyland Resort in early December and we did not have time to do everything. We roughly spend 3 days in Disneyland and 2 days in DCA and that was rushing around, not giving time to take in the details and the shops, etc.
I swear, by some of the comments people make about "taking in the details," you people must walk around the park like it's a museum. The details are to immerse you into the experience, not be gaped over like museum artifcats. I was at Disneyland on Tuesday, and not rushing, I went on most attractions within the 5 hours I was there. What I didn't get to I did on Wednesday. But I agree with you that on an average day I would have needed two days to experience everything. I don't need but a day at the Magic Kingdom at WDW. Disneyland just has so much more.
DCA, on the otherhand (thanks to single-rider lines), even on a busy day I wouldn't need much more than half a day, if that. I can only think of three attractions with themed queues, and of those only two were completely themed (Soarin' and Muppets 3D), the other was only themed close to the boarding area (Mike & Scully). So "taking in the details" there isn't as involved as it is across the plaza at Disneyland.
Bottom line is there is almost the same amount of attractions crammed into the 2 Disneyland parks as there are in the 4 WDW theme parks. So I think that a trip just about as long as you would spend at WDW would be in order. Next time we head out there we'll be spending an entire week!
Much like Disney World, it all depends on crowd levels. Last week it took me two days to experience both parks, but I was there five (which I think was just right). And I certainly didn't rush. Disney World takes longer because the parks are bigger, further apart from each other, and it takes time to travel to them. But in essence I agree that Disneyland and WDW take roughly the same amount of time to experience.