Although I see the point in removing a symbol for one faith from public land, separation of church and state being the crux of the matter (pun intended), it is a pretty stupid lawsuit. I suggest the property be sold to a private non-profit, or declared a national landmark as is.
Just for reference, here's a photo of part of the Pacific WW2 Memorial at the Presidio in SF. No cross, but a reference to our Lord.
