While Nader realized he would lose the election, he made a big point of trying to capture 5% of the vote and also trying to raise additional awareness of his core agenda.

Winning 5% of the vote would have enabled the party to qualify for Federal Election Funds in the following election. http://www.fec.gov/press/bkgnd/fund.shtml

Dont forget that these days $$$ = share of voice.