Sea World's problems are largely out of their hands. Vacation time is a zero sum game--vast majority of guests have a limited number of days in Orlando, and are only going to pick one theme park complex per day. SW gets hurt on two levels here--first, there's a lot of cool stuff coming (F&F, Nintendo, Star Wars) that makes other parks around town more enticing than theirs. Second, the two big boys make it so much cheaper to buy a third or fourth day with them rather than a first day at SW--this discourages "cross-town park-hopping," for lack of a better term.
And that's just the big boys. Andretti Park, 5 minutes away, is a thing. Successful thing? Who knows, but potentially. SkyCoaster may yet happen. The biggest issue--the allegedly still coming thrill park (with 6 Flags as a partner) up the street at Festival Bay/Artegon. Any of these would be a cheaper than Disney day of thrill rides which is the one market SW can still compete in. None a factor today, but in 5 years?
(This is all assuming of course we don't get another economic downturn or, knock on wood, catastrophic Orlando event, which affects all the parks, but SW most because they are the least flexible--can't bribe guests with free dining and the like. One bad news day could accelerate the timeline.)
At the same time, the area around SW is turning into a west-side version of Baldwin Park. The land it sits on grows more valuable as housing or retail every day.
Is there still a great deal of value in land zoned for theme parks? Of course. And I doubt Discovery Cove or even Aquatica go anywhere--they are small, busy and presumably profitable. But it's naive to assume SW will always be there. If you don't believe me, take a drive up to Posner Park in Davenport and check out the names on the street signs, or the giant overgrown parking lot in the middle of nowhere.