I guess its a tough call to make, but I think that DK is making the right decisions. 9 times out of 10, in the showroom the owners also discuss mods made to the vehicles, which would make the vehicles that much more attractive to the criminal classes. Since Strife's HSV appears to be the latest vehicle, it would probably be a prudent measure to ensure that other people's hard earned money, pride and joys, and blood, sweat and tears aren't viewed by randoms with an intent to steal. No offence intended to random visitors who arent intent on stealing vehicles, but I guess, by definition, The Showroom would be like a one-stop shop for a thief looking to ghost a vehicle or strip it down, etc.
I hope the people who have had vehicles stolen / people who are yet to have their cars stolen (god forbid) have them retrieved in lickety-split time.