Disney's waterparks are more of an add-on attraction at the Walt Disney World Resort. They serve their purpose but aren't the main attractions like the four theme parks or Disney Springs is.
It's unlikely that Disney will make sizeable, notable investments in either park. However, they have been spending money in the parks lately on maintenance and did build a sizable family raft ride in Typhoon Lagoon.
I still can't believe that Typhoon Lagoon remains closed.
I think this is the key point, at least for someone like myself who generally fits in the 'extended stay once a year' category, they are nice added value but I'd still be coming if they weren't here. On the odd occasion I do a truncated trip, the water parks will always be the first thing to drop off my schedule.
I feel like they did such a complete job in building them from the off, for the very purpose that they wouldn't really need to touch them outside of general maintenance - an approach I think has been done with Volcano Bay in preparation for UOR becoming more of an extended stay location when Epic Universe opens.