Sure double points will boost sales. I pledge to buy many tickets if the same unlimited double points promotion returns!
But it may be a double-edged sword. Some might actually travel less, because the points were so easy to get.
It is like raising the commission for a salesperson. Will he sell even more to get a really good months pay, or will he sell less, because he values his spare time higher than more money? This dynamic is not easily figured out.