any tax you place on haycubes to try and incentivise interaction with vets is purely a tax on newer players, who are both A) more likely to travel around to see all the cool shit in tahoma and B) less able to pay for haycubes.
locking things behind interacting with seldom-played whitelists elevates these people sure, but it also results in a headache for literally everyone else.
"sorry gang, we can't hunt the outlaws, I gotta go see the vet so I can feed my horse john" - statements dreamt up by the deluded