I was a member for over 4 yrs with my wife with LGC and i can say,be carefull,Yes police are there and yes plain clothed officers are also,what you can expect is a citation/defect noticed issued from the pictures these officers take at the events and process later.
I wasnt going to say anything except as this cruise builds momentum perhaps your best be mindfull,your car is 100% roadworthy and engineered,carefull of the tyres.....its happened to many of a car sitting there ,bonnets up,then a few weeks later in the mail.
We never went to many events with our gts ,but always my wifes stock hg premier for this reason.
Goodluck it is usually a well organised family event
cheers anthony