It is important to realize a township's motivation for not letting bikers in. When a town builds a public park they work with one of the numerous builders out there, some of which are good, and do good **** and some whom are for the most part concrete jockey's who don't care what they are building. There is around skateparks a collective mythos that bikes do alot of damage to parks, then builders who really don't know their **** or concerned memebers of city councils who read about other parks which ban bikes, just go ahead and ban bikes in the parks. So you see it isn't so much that anyone gives a **** about what the **** a bunch of teenagers are doing on bikes as much as they care about enforcing a rule, justly or unjustly established.
I believe the wisest plan of action would be to get all the BMX cats, and your parents(yes...ugh...parents) and go in front of the city council and ask that the issue be adressed. By involving one's parents whom support you, you appear less as angry-deliquent youths, and more like concerned citizens. Good Luck.