Gas prices dropped again last week and are sitting at nearly four year lows but will it be enough to save Christmas?

First the good news. According to AAA the average price per gallon in the US is $3.04. That's a drop of 6-cents per gallon over just the last week. Gas prices are down more than 10% since Labor Day, much lower than where they were this time last year. If prices hold and all things remain equal that drop will lead to $50 billion in additional fuel savings over the course of the year.

Now the bad news: according to informed sources Santa's sleigh runs on good will, not unleaded. For most of us the price of gas per gallon is pain-weighted to the upside: we feel higher prices but tend to ignore drops, at least when it comes to other discretionary spending.

If you run an Internet search on gas prices and consumers you'll get back a weirdly high number of results from early 2012 when it looked like gas could go over $5.00 gallon. Wal-Mart and a host of other retailers were pointing to gas prices as a key factor in their inability to grow the top line.

Now that gas is 40% lower its crickets, both in the malls and on the retailer conference calls.

So what happened? The truth is gas only makes up about 5% of what we spend every year. That's a big chunk, as a whole, but do some math on what these incremental moves in gas mean for a budget and you can see why it's not much stimulus.

For every household dollar spent slightly less than a nickel goes to gasoline. When gas prices fall by 10% it means you have about 1/2 of one penny more per dollar earned to spend on things other than gas.

According to the U.S. Bureau of Labor Statistics the average consumer spent $2,418 on gas in 2013. Pro-rated over the holidays that means the drop in gas will give us, on average, about $20-$30 extra bucks to spend on gifts or maybe dinner and a movie for one.

It's better than nothing but if you're expecting gas to mean a booming Christmas just keep driving until you find a better reason.