Rich Suttmeier of ValuEngine.com warns that using cheap dollars to speculate on other investments can backfire if the dollar rises in value and investors all run for the exit at the same time. "When it ends, it will end badly."

Also driving stocks higher:

Performance chasing. "Investment managers are playing 'benchmark bingo,' " says Sam Stovall, chief investment strategist at Standard & Poor's: "They only have two months to tie or beat their benchmarks," by which their performance is judged.

Prospect of better profits. The weak dollar is a plus for U.S. firms that do business abroad, Bittles says. A cheaper dollar makes U.S. goods more affordable to foreigners. U.S. firms also get a boost when they translate foreign-made profits into dollars.

Seasonal trends. Stocks have entered the bullish six-month period from November through April. Since 1945, the S&P 500 has gained an average 6.6% then, vs. a 1.4% gain from May through October, Stovall's data show.