Personally don't see the onboard prices to be that expensive. It's only what you pay on a night out in a major town or city. Norwegian even sells full wine bottles for a similar price to what you would pay in a soul less chain restaurant. The 330 ml cans are very poor value but it doesn't deter people buying them. If people are out to get drunk they'll do so regardless of price.
Contrast that to a full service airline. They give their drink away for 'free' yet I'm sure it doesn't incentivise people from not getting merry before hand or bringing their own alcohol onboard.
Flying into Spain the police are slow to respond and usually couldn't care less. Last time they told us they couldn't do anything as the aircraft is not EC- registered and therefore they have no jurastiction. So in those instances cancelling their return flight is as much as you can do.