The U.S. brands of right wing extremism are something that's likely more troublesome in the long term than whatever sugar high the European right wing(s) might get from the economic troubles.
Luckily, Americans have troubles crossing the English Channel language-wise.

Another long term problem with right wing ideology stuff might stem from Russia, Belarus and the Ukraine. Nationalism and jingoism appear to be part of what fills the void left by communism in those countries. This could turn ugly sooner or later (even more so in East Asia, where the Chinese, Koreans and Japanese have some outright ridiculous nationalistic ideas).

The only area in Europe where the economic crisis could give a decisive push to nationalism is in my opinion Catalonia.