SmokedGoudaThere festivals are wack and not too much of a problem, but there only source of income/an economy are weed shops
If you're talking about the country Netherlands and the way they deal with weedshops/coffeeshops, its really hard to estimate the percentage of the gdp it represents.
The Dutch "IRS" (tax authority) doesnt differentiate between weedshops and other restaurants/cafes. The percentage of gdp for all restaurant and cafes as a sector was around 2.5%. The Dutch bureau of Statistics had a rough guestimate that 1% of the Dutch gdp comes from illegal activities. Seems quite low, but they probably dont have an extensive dataset on this subject to do accurate statistical research.
Weed/hash isnt legal though in the Netherlands. But the sale and consumption of small quantities is decriminalised. Everything else in the supply chain for the weedshops is still very much illegal. So growth transport and storage are all still illegal. And for the illegal part of it, it is hard to exactly measure the value it adds to the economy.
The only reason it is because some of the more Christian oriented political parties still put the label of drugs upon it and block every idea legalizing the 'weed industry'. Only means that the government is missing out on some serious tax revenue and currently spends quite a bit on battling the illegal growth and distribution (supply to the shops).