Disneyland and DisneyWorld are very different places.
Disneyland in California - 2/3 days is all you need. There are two parks next to one another, a bit like DLP. It's the original.
We went this summer as part of a two week holiday. We spent two days in the park, though 3 nights in the hotel. To explore other parts of the region we stayed elsewhere as its a fair bit out, compared to everywhere else we wanted to go.
DW is much larger, and in an area close to other theme parks. In the past we've done two weeks a few times but not tend to only go for a week.
At DW there are four theme parks and two water parks. It is almost impossible to do all the rides and attractions of all the parks in one day. In addition there are the two Universal parks - again you can't do everything in them in a day each, not without paying extra for Express. There are other places you can go to also.
When we do a week at DW we do a theme park a day - 6 full days, 6 theme parks. We go in February generally for a week so don't bother with water parks.
When we've been for a fortnight (so 13 full days) we tend to go in the summer where it is very hot so prefer to go slower. So we do 6/7 days at DW parks, a half day at a water park with half day at a mall) 3 days at the Universal Parks, a day at Space Centre, and a free day to go to either the beach (bough often too hot for me), relax by pool with dinner at Disney Springs or something.
However we love roller coasters and theme parks. 14y dd is a huge fan and would go every year. It's also a very easy holiday when you've an only child - all entertainment is provided, she is excited and happy and wants to spend her time with us doing the rides and shows.
We go again for a week in February 2017 and taking dd's friend - she's never been long haul, never been to the US and never been to a Disney/universal park. She's very excited especially now we have our restaurants booked :)