Ok, I addressed the exercise part above and I think restoring former sludge ponds to nature, the funding and staff for species and habitat stewardship, etc in exchange for 2% of the land for trails is a fair deal. If others do not, don't sign.
These parks can and do coexist with nature. Santa Clara County Metcalf Motorcycle park has won environmental stewardship awards.
As far as your issue, I'm not sure having the tags helps because law enforcement didn't witness it except it may get them a letter sent like the CHP does with similar complaints. The CHP may have jurisdiction off-highway, I think they do. A call couldn't hurt.
As far as state parks it may be a little more difficult to deal with because the Off Highway Recreational Vehicle (OHMVR) Division is a separate division from the main State Parks as is Boating and Waterways. This is changing as the State Parks is modernizing and consolidating into one unit.
I don't know where you live or what park it is but here are some things you can try if willing.
1. Call and escalate your concerns with the local State Park up to whatever higher level you can all the way up to the Director's office.
2. Contact the OHMVR division with contact info at the bottom of the page at
http://ohv.parks.ca.gov and let them know. They will take it seriously as it affects the whole sport and the Division's reputation.
2a. PM me your name, email, city and the park name and I will put you in contact with the Commission Chairman directly, Cc'd on an email.
3. the OHMVR Division has law enforcement grants for situations like this. Go to your city council and tell them this and ask them to apply. If they are too lazy fill out the form for them and get some others to speak in favor. The county can apply too. They can hire LEOs and purchase their own vehicles to catch these guy before they get in the park. Local LE may be able to work out a deal where they help patrol the park. A job I wouldn't mind having, The next grant cycle is in April.
4. It may seem counter-intuitive to you but advocate a for a different area or a corner of this park being opened for OHV use so people have a legal, environmentally planned and maintained park to ride in. More and more cities and counties are realizing that if you give users a place to ride they won't have to break the law and are looking at opening parks using state grant funds. State parks is contemplating sharing more activities in the parks just as at Holister Hills OHV park has mountain bike trails. This is where electric bikes would shine without noise and pollution.
That's all I can think of for now. Good luck.