A tax cut is when government does not take money from people in the first place. A spending program is when the government collects money and then gives it to someone. Even if it is the same person, it is a government program if the money is cycled through Washington. Rebates have no stimulative impact on the economy. The notion that consumer spending drives the economy puts the cart before the horse.
Production drives the economy and people then use the income they earn to both save and consume.
If Keynesian economics had any validity, the U.S. economy would have boomed in the 1970s. Even Keynesians should reject rebates since there is no increase in the amount of money in the economy. This is because one alternative to rebates is debt reduction. This is the common sense notion that tax cuts help the economy by encouraging people to produce more. The economic stimulus occurs because the tax penalty on productive behavior is reduced, not because there is more money in people's pockets.