You measure the value of VIP treatment in the weeks after the event, not just on the day itself. Ask VIP guests personally for feedback via a phone call or a brief chat. Then look at the business outcome: new conversations, deepened relationships, opportunities that weren't there before.
Also keep track of which elements of the VIP treatment received positive reactions and which were barely noticed. Build up that knowledge over multiple events. Welcoming VIP guests well is not a one-off achievement. It is a skill you refine by doing it a little more consciously each time.