Do promotions help retailers’ bottom line more than investments in social tools et al?

Data from comScore as reported in the Wall Street Journal shows holiday sales up 4% over last year.  Not bad considering the economy. But the growth appears to be driven largely by a huge increase in promotions:

«Data from Shoplocal.com show that online retailer promotion activity is continuing at a high rate with the number of offers in the last week up 21% versus a year ago,» said comScore Chairman Gian Fulgoni.

The strong sales numbers won’t mean much if the January headlines are all about the carnage from over-discounting.  (Remember the joke about making up for negative margin on volume?…)

I’d like to see an analysis that compares the cost of all that discounting to the cost of tools that could drive equal sales volume without compromising price.  For example, for a small percent of the cost of their holiday promotions, most retailers could dramatically expand initiatives like social shopping.  And in the end, their bottom lines might look a lot better.  Please comment if you know any work that looks at this.