I would first look at what do I have direct control over, what can I do regardless of police cooperation.
* Erect a vehicle proof wall at least 3 ft high (like reinforced concrete 1 ft thick, or at least mortared rock) at the very edge of your property to prevent any accident spilling over into your yard. This is for safety as well as protecting against them claiming that portion of your property from repeated use and you not preventing them from using it.
* Consider getting a truck or van that is much bigger and uglier than whatever they drive. Again for safety in case they do slam into you out of control one day, but also for intimidation. When I had an UGLY brown American Motors Hornet NOBODY messed with me in the lanes. It was so fugly nobody else wanted to be wearing any part of it from a scrape or bounce.
* Definitely get a video surveillance camera and/or 8 mega pixel still camera with 10x zoom. The video will establish frequency and severity of their activities, and record any specific event that gets out of control. Keep the still camera in your vehicle to snap license plates and any situations away from the home (down the street).
* I liked the idea of the "friendly display of shotguns." In no way do you brandish them, but you just tote them around the yard, maybe on a sling, or have friends over looking over several one afternoon when the punks are likely to be burning up the road. Country boys (I grew up fairly rural Washington state) generally appreciate another guy willing to protect his own but not looking for trouble either. All they need to know is that you have shotguns handy and are likely to not hesitate if anything ever escalated. Or post a home business sign "Gunsmith, by appointment" or "Ammo for sale, free samples!"
* The other idea was good about trying to chat them up. If you can find common ground then maybe they will respect your concerns and place more. Invite them to look at your "hot rod", or ask them for a recommendation for a shop or something. Fishing? Hunting? Sports? Basically telling them "Yeah, I like hot cars (or ______ ) too, I have nothing against a guy liking to jump on it once in a while." And then perhaps you can suggest a better place for them to race, "When I was a young man we used to go over by the landfill to jump on the gas. No houses or families around there." Or, at least let them know you just appreciate them doing it in front of your house.
And of course, after exhausting those things I have control over, then I would be working the neighbors, even the ones at the other end of the street or other parts of town they race at, too. And working with the police. Maybe try to find a place the kids could have their fun more safely and try to get the neighbors and polce to support the idea of telling the kids, "Over there is OK, but not any where next to houses." Come on, if you are in a small town in the country then it is only a few minutes to get out of town and away from all houses, right?
I lived in a small town in Iowa in which the kids of local "rich" people got away with vandalizing and burglarizing stores, harassing pedestrians and street racing. The cops plain said their "hands were tied and we aren't going to try to arrest any them minors." You either had to move, stay out of their way, or what I did one night after our bikes were vandalized is walk through the town square and up and down the main street (literally) with a bike chain in one hand and a scowl. I don't know if I would have hit any of them if I had encountered any, but they cleared the heck out of town that night. Never was hassled after that. Probably not the smartest thing to do, but I was steamed and really didn;t give a rip about consequences, I just knew I was NOT going to put up with their crap one minute longer. I kind of sensed the police would look the other way and let one of the brats take a shellacking as long as it wasn't too serious. YMMV
