Here's a paper & a couple excellent blog articles on the topic: http://www.sciencedirect.com/science/article/pii/S0966692308... http://usa.streetsblog.org/2013/08/14/jarrett-walker-empty-b... http://www.humantransit.org/2009/12/yet-another-transit-isnt...
From the paper's abstract: "Public transport faces an increasingly intense conflict between patronage goals and coverage goals. Broadly speaking, patronage goals seek to maximize patronage of all types, while coverage goals lead to the provision of service despite low patronage – to achieve social inclusion objectives for example."
I think that this article is missing a huge part of the success of the Denver region. It is not just the RTD but many other factors. The transit efforts are not in isolation.
Denver is a sub-urban city, but they have strongly revitalized their downtown and older districts. Downtown has the 16th Street outdoor shopping mall, all of the stadiums for major sports, convention centers, museums. The amount of new housing units that have been built within walking distance of downtown is huge.
The article briefly mentions some of the projects in LoDo as if they were all part of the RTD, but LoDo had been rejuvenated long before the current rebuilding of the Station.
And there seems to be thought into not just rebuilding the old downtown, but I see this around the Tech Center and Stapleton.