One of the Peninsula Transit Study's recommendations was for the city to adjust parking rates according to the time of day. San Francisco is about to try doing this on a broad scale, and the city's put together a good overview of how it would work:
In the longer term, data on parking rates and utilization in different neighborhoods will give planners and developers a better idea of how much new parking should be added with new development, instead of relying on arbitrary zoning codes that were developed in the 1960s. That would lead to lower costs of renting housing and office space in the city.
Of course, in order to implement such a program, Portland would need a business-savvy, innovative manager for its acres of public parking real estate. Personally, I'm not holding my breath.