Maybe we are looking too hard for a Dallas answer. Nationwide the the DOT's 2009 Household Survey showed only 3.7% of commuters used transit. Average transit time was 50+ minutes, average car time was under 25 minutes. The Brookings study showed that for 4% of possible commuters the transit time was under 25 minutes. Coincidence? Could it be that people will use transit absent other factors when the time is the same or better? Since the difficulties on reducing the time difference are generation time framed solutions, we'd have to look at the other factors.
It's cost of car ownership, not cost of gas, that drives ridership. Instead of wrecking the economy by raising energy prices, why not double or triple license and registration fees, add surcharges to auto insurance for adults, but especially for teenagers, have rigorous inspection criteria in urban areas that would difficult for any 5+ year old car to pass, and jack up the tolls and tickets for violations?
DART is bad, but better management may only tweak the results. That improvement will not likely overwhelm more citical factors that are independent of system operation.