I get the history, and understand the importance of the biker trade. But then, you used to be able to park in a lot of places for free. Times change.
The enforceability/cost is a genuine pitfall, I agree.
It may change the demographic of the visitors rather the spend. When it’s full of bikers, no one else can get in as there isn’t a huge amount of parking close to the “front”. They are trying to reboot the area and make it more a year round place, and when the weather is bad, the bikers don’t turn out in any great numbers at all. And although I’ve never heard or seen any trouble, if you are of a nervous disposition and passing through then all the bikers can appear intimidating.
Most bikers would still go and pay up. For those that don’t, someone else will take their place and spend their money.