Supposing the two campaigns/parties have about relatively equal budgets, which has been the case since about 2000, if you are confident your voters aren't going to flip, you can be much more assured in not over-investing in areas you have secured and go on the offense. I think in this regard the heavily blue areas are a safe bet. Studies consistently show that one of the most effective means of political communication is person-to-person, the traditional canvass, phone-banking, and talks between neighbors. Television and print advertising is expensive and inefficient. People just tune out the campaign ads and throw away mailers.

If the DNC/Obama wanted to put at a minimum 2 organizers for 1 year in 4000 counties at a supposed 100,000 a year including wage and support resources (office etc.) the total cost would only be 64 million. Those two organizers could recruit volunteers and raise funds locally to support those volunteers. Even at a conservative estimate of $100 million, which would allow more organizers in bigger counties and allow for cost overruns. The expense of such approach in a campaign year in which an estimated $500-1 billion is going to be spent on each side is minimal. Such a strategy empowers the grassroots and creates an organizational structure that can survive off-years.