You can't possibly compare Poland to Bulgaria with 1/8 Poland's GDP and 17% its population. For Bulgaria the Euro is completely fine, as the Lev has been pegged to the Deutche Mark and later the Euro for ages. It's exports are basically raw materials and grain. Most of the other stuff they produce is sold domestically. I think I've only seen Bulgarian sunflower oil, mineral water, ketchup and pasta in stores outside the country. For a state with so feeble exports and a pegged currency it really doesn't matter, only adds up currency conversion fees. They might want to attract more tourism and investments.