Don't think you can sue them.
Regarding the defect notices places on parked cars, haven't looked at regulations (its 11:56pm so not in a mood to research), but definitely something to look at to challenge. An argument could be put forward that they were not driven to the event and a tow truck was used (though, due to strict liability offense, evidence of a tow truck use might be needed (receipt or witness being the driver of the tow truck borrowed). Once again, haven't researched the law, but just some ideas.