It all depends on where the chain forseas themselves making the most profit. Water parks seem to be coming back in style, judging by all the additions and new parks springing up around the country. WW was almost to a stage where they needed to update it or let it die before they started rebuilding it a couple of years ago. It still doesn't hold a candle to most parks, even those in the region, but that might change with a good slide tower and increased theming. A lot of people seem to be flocking to the water parks as cheaper alternatives to the big dry parks.
SDC on the other hand doesn't have as much potential to increase their revenue right now. Even if they spent millions on a big new ride they might see less attendance due to the number of people striking trips to SDC from their budgets. DW is in an area with more stable jobs I guess, or at least a much bigger market.