I am not sure what time period you are referring to as to campaign spending. Obama kept campaign offices going in the major metros from 08 to just last week. If that spending is included, then the Repubs got out spent badly in time and money.
Sowell is usually on point, but this time he is underestimating the ground game. Obama and the Dems are cynical realists and know who will vote their way. Several million non-traditional voters were signed up and list compiled for this election. Obama knew he would have buyer's remorse amongst older and white voters. So he ignored them, calculating some losses, but he more than made-up those loses with minorities, single women, and the young (each group increased its share, especially in swing states)