Well you'll be happy to know that no taxpayer dollars are used to fund this expansion at DIA or any commercial airport expansion anywhere in the US for that matter.  Airport projects like this are fully funded by the airlines that operate there through rates and charges.  Which is partially why United, Southwest, and Frontier were against the $1.8B renovation project for the main terminal.  Because they have to foot the bill directly but the project doesnt really bring them more business.  Now adding additional gates to the airport allows the airlines to bring in more flights...which means more passengers and a way to help pay for these projects.  So to answer your question, no, this is nothing like the boondoogle system that professional sports owners have worked out for their stadiums.  Airports for the most part are totally self-funded baring various federal grants for things like noise abatement and environmental issues.