It might be a good revenue for a city! I never thought of it that way.
I have read about several parks in the New York and New Jersey area that are owned by the municipalities. I don't live in that are so I can't confirm this. In this case it seems like a win-win. In this case Vallejo doesn't have to deal with debt or liability and Six Flags keeps all the revenue. I haven't visited this park, but maybe this will create the impetus to overhaul the park like they have been saying they have been/are doing to their other parks since the new management has taken over.
When the park was still Marine World/Africa USA, and still owned by the Marine World Foundation (with Mike Demetrios having the primary controlling interest), the arrangement with the city of Vallejo was essentially the same: They loaned the foundation (and thus the park) big bucks, and were also granted controlling interest that would persist until the debt was paid off.
When the original park started to go downhill, the MWF ended up defaulting on the loan. The only way the people involved could get out of the situation with their skins (and bank accounts) reasonably intact was to, essentially, sign the entire park over to the city.
Since the City of Vallejo had not the slightest clue about how to run an oceanarium/wildlife park combo, they started looking for a buyer who (supposedly) knew what they were doing. This, if I recall correctly, is where Sick Flags stepped in.
I'm sad to say that the current park is a horrible travesty of what it once was. I still believe it would be better for the few animals that remain (and, most likely, the park's attendance figures) if they would simply send the rest of said critters to proper facilities at other oceanariums and zoos, and finish turning the place into JATP (Just Another Thrill Park).
I would add that the park will still likely be a revenue source for the city of Vallejo, in the form of property taxes.