As far as the problems with interference from park flyers, it is no more probable than interference from someone flying a mile or so from an operating field.
Our previous club field had occasional bouts of interference on certain frequencies. The interference was very spotty. We could go weeks without problems.
Happened to mention the problem to a Ham I knew at work. He asked what frequencies we had the problem , and when I told him, he became a bit concerned. He apologized for at least some of the problem was caused by him and his son. They were flying RC at a local community college field less than a mile from our field. In fact, there were times you could see planes in the air at our field from the college's parking lot. And with the big gas engines, you could even hear them.
He and his sone joined the club, and finally realized how much easier it was to learn to fly with an instructor, and how few and far between the near crashes and crashes were when there was frequency control.
There were other people flying there who exhibited the I don't give a _____about anybody else attitude after being approached by this new member. Some people just don't want to respond to common sense, and have no respect for other people. Our officers approached the college plant manager and security, and discussed the situation. The college then banned ALL RC flying on their property. This did not affect the kite flyers, the control line flyers, nor did it stop the college from setting aside monthly Sundays for the area FAC free flight people. They intelligently responded to the highest liability potential.