Iceland went basically bankrupt less than 20 years ago, saying they're doing "extremely well" is either misinformed or disingenuous. They do ok on some parameters, bad on others, and their small size makes them fundamentally weak to global economic winds. EU (and particularly Euro) membership would not magically solve all problems, but could make some things a bit clearer and more reliable.

Sadly, the voters have spoken and so they'll have to continue doing what they do now.