I've taken a bit of time out from kiting, but when I did used to go across to my local spot (Bidford Meadow, Bidford on Avon in Warwickshire), I can honestly say that we have never had any complaints from anyone. Most people stand and stare in amazement and they seem to like the kites being in the sky, I suppose as long as the field isn't too crowded anyway, which it never is. I feel for ya Johnny, it is soo frustrating when you want to participate in a sport that you love and other people totally ruin it for you. My advice would be, as previously suggested, get a few of your crowd up to the council and see if you can speak to anyone regarding the issues that you have. If they won't speak to you send them letters, email, call them and generally pester them until they listen and come to a compromise.
If that fails then speak to the local media, as I'm sure they will think this is a story worth writing about (COUNCIL IGNORES YOUNG PEOPLE). Perhaps you could even ask the people who use the park what they think of the kiting activity, at least that will show both you and the council what the majority think and it will show the council that you are using your initiative and have a genuine love for the sport. What the hell, the council may even allocate you an area of land to use...
...well we can always dream
I hope this helps.