Not that I can remember. At least not in the last 10 years. I guess they don't feel the water parks need to be expanded because they do quite well whether they are or not. They do add little details during rehabs (such as one year, they added Ice Gator's house in Cross Country Creek where he sneezes on you), but no major slides.
I don't think it's Disney's intent to build more thrill slides in TL or BB, because they really don't have to. BB already fills to capacity on most hot days and TL takes the overflow. In fact, there was so many people enjoying the water parks, that Disney considered building another one, but haven't heard much on that since 9/11. Since both parks are included in most passes and those that live in Orlando have AP's or even water park AP's, both parks enjoy guests from WDW and Orlando/Kissimmee (who use it as their beach, since they are 50 miles from the real one). They are conveniently located and accessible through internal transportation as well. TL & BB are also places that are considered a supplement to the whole trip, rather than a full day's entertainment. Somewhere to take the kids that is a little more exciting than just the resort pool.
I'll venture to say that Wet and Wild has a lot more guests that pay the regular admission price and consider it more to be a thrill park, but in doing so, want to have enough to do for a whole day. They are also at the disadvantage that they are not within a complex and so getting there is something that people have to plan to go and then drive there separately from other entertainment venues. For instance, it's quite a hike from WDW to Wet and Wild. Of course it's a shorter distance from Universal, but still quite a hassle. So it attracts new people and day planners by putting in new attractions. Nowadays of course WnW is bundled with passes for Sea World and Universal Orlando, but still have that problem of location. It's also not shady at all, so in the summer you have to have much more water attractions than BB & TL to keep people from dying of the heat. Thus getting repeat business hinges on new attractions, where TL & BB doesn't.
There is just two different marketing philosophies. WnW considers themselves a thrill water park. Disney considers TL to be a place to relax and BB a place that covers both fairly well.
