Checkout the May/June issue of "Paddler" magazine there is a great article about the sucess (read that $$$$ to the community) of bringing a Playpark to a town.
In reguards to help/hurt boating that depends on your viewpoint.
Helps by giving boaters a centeral place to learn river skills with others around to lend a hand as needed as aposed to losing it going down the unknown river, making boating safer overall. Brings $$$$ to the local boating bussiness and others.
Hurts, any time you have a place where a large amount of people gather you will have litter, ground damage look at Golden/Union where the grass is wore to dirt.