Wetlands should not be filled. They will eventually flood again, the open space being proposed is great. The reason we have flooding in JC and other urban area is - too much black top. The rain has no way to go.
To my knowledge these acres are not wetlands. They may have been 150 years ago before the were filled in, but not in a long time. Ball fields would absorb rain just fine, they're not black top!
The reason most state parks do not have ball fields is that most of them are located in communities that have plenty of open space for parks. We do not. LSP has 10x more open space fenced off from the public than there is city parks in all of JC. We are far below what planners agree is minimum per capita parkland even if you include LSP, without it we're in the toilet.
Most of the park is land fill, pre railroad, way back, but I do recall about 15 - 20 years ago, there was even more natural marsh land behind the interpretative center. Salt marsh is/was the natural state for the area.
"LSP has 10x more open space fenced off from the public than there is city parks in all of JC." State your source of information; I doubt your original assertion is correct.
You conveniently overlooked my post detailing Ed "Faa" Ford and the newly constructed and very large Berry Lane park sports fields located a stone''s throw from LSP. Additionally, there is also Lincoln Park, Pershing Field, and Washington Park, that all have ball fields, athletic facilities - all very large muni/county parks, located in Jersey City.
Then there's Fisk park, Colgate park, as well as many smaller parks, peppered throughout the city that have basketball, tennis courts, etc.
Jersey City is roughly the same size as Manhattan in square miles - actually slightly smaller. You mention Central Park - unlike that great park - Jersey City's park sports facilities do not have a wait list/signup requirement to use. Quite the opposite.
That is, to add more sports/athletic fields to a LSP is a waste. There is already a sufficient amount of supply to meet demand. Actually much more.
Like I mentioned before the State does not do sports fields. Unlike your "located in communities hypothesis", many of the state parks are located in remote rural(ish) parts of the State.
You'd have leave Hudson County to figure that out and travel a significant distance to see firsthand at another/next state park. The Division of Parks & __Forestry__ have an excellent website (and iOS app) that will tell you all about the state parks, including their amenities, like here:http://www.state.nj.us/dep/parksandforests/parks/parkactivity.html
What the urban area needs is more of what is proposed - natural landscapes and land preservation. That is what NJ State Parks are all about and is in much less supply in Hudson County.