LOL Cal, it's fine if we disagree!
Soak City is not doing well, I've heard that too, but then again Knott's itself does not do near the business of Disneyland. A water park attached to a theme park is only going to be as strong as the theme park itself.
Raging Waters and Hurricane Harbor are each pretty far from Disneyland, not to say somebody in Southern Caifornia can't easily get to them each, but the point would be to expand the Disneyland resort, and give people who like water parks another reason to stay on property.
I'm not saying Southern California doesn't already have water parks, that's not the reason to build one, the reason is that Disneyland does not have one. Many annual passholders wpuld add on to a DLR water park, but not to many of them have annual passes for the other water parks. Sure some do but not a very large majority. Why? Because the best water park of them all is in San Dimas. Sure just as many can drive to there as Disneyland easily, but nobody is going to make a routine trip unless they are extremely close to a water park. Many go to Disneylabnd resort once a week or so, not to many go to Raging Waters that often.
Although there are many small water parks, there's only those mentioned water parks are of any real significance. Heck if Disneyland used those reasons alone, they would have never built DCA, since Southern California is full of theme parks as well as water parks.
The entire idea of the resort expansion, was to get more business, and let non locals hopefully spend a night or two at the hotel. You have to cater to many different tastes to accomplish that.
For those that prefer the beach over a water park, be my guest! Disney really does not mind whatsoever if you leave the resort for a day, the own Birnbaum guide to Disneyland recomends places such as the beach, San Diego, and Universal Studios. Why? Becuase they know even a two park resort is not quite enough to keep most 1 week visitors busy. But you can bet the WDW guide by the same publisher, makes no reference whatsoever to any other Orlando activities outside of WDW. Why? Becuase they catered to the different tastes, by adding water parks, as well as golf courses, activities at resorts, etc. Of course Disneyland resort will never be the size or variation of WDW, but with a water park, and an eventual third park (hopefully), they are getting there. Nobody ever dreamed 20 years ago, a parking lot could become a second park.
Orlando is full of non Disney water parks as well. We have Wet and Wild, the most sucessful park (similar in theory to Raging Waters), only here it's in the same city, Orlando. Yet still many people prefer an on site water park. The water parks still fill up at WDW quickly, even though there are other water parks in the city. And in Orlando the competition even though it' all in the same city works just fine.
So if one city can do it in Orlando, I don't think Anaheim has to worry about the rest of Southern California pulling away it's business too badly.