This is an interesting debate for Portland. I've always found parking to be VERY cheap and easy in Portland no matter the time of day. Part of that has to do with the size of Portland, more of it has to do with the fact that there are lots, garages, and street parking spots everywhere.
It looks like that rendering of Commercial St. has a trolley which, quite frankly, would seem to be pointless. commercial street stretches from the waterfront fringes of downtown to pretty much nowhere. It's actually a funny drive once you pass Becky's diner heading away from Downtown because there is so little there. Areas better served by a trolley would be Congress St. from the Eastern Promenade to Maine Med. (though I doubt they could make room for it). and potentially Forest Ave from Woodfords (or Morrils even) to Cumberland or Congress. A Commercial St. trolley would be more of a tourist attraction than a functional means of mass transit.
That being said, while many people use bikes, Portland doesn't have the size or density to encourage many more people to use bikes regardless of parking costs. I would bet that most of the people in Portland who would potentially use bicycles already do. An increase in parking prices will not encourage the workers (who commute from quite some ways sometimes) to bike or bus it.
Furthermore, the METRO routes don't extend far enough outside of town to be of much use for most of the commuters. Portland is at a disadvantage in terms of encouraging people to seek other methods of commuting because the lack of alternatives. Bus routes don't extend beyond Westbrook, Falmouth, and S. Portland, yet many people commute from outside those areas. There's no train for commuters (the DownEaster is little more than a fun ride for tourists plus unless major changes are made, it'll be out of service by January 2009), and few long distance bus alternatives.
While I don't think discouraging driving is a bad idea, I don't think Portland has the means to work with in doing so. Seriously, how many people from Scarborough are going to ride their bike to work in December because parking costs $15 a day instead of $10? It's too small of a city with too few alternative options for commuters. Besides, does Portland really have a congestion problem? I've been going to school in town for 4 years and never noticed anything that resembles a traffic problem.
