The Economics of Parking Lots
As in all economics, however, there is another hand. Namely, parking lots are exceedingly ugly. Putting parking lots and parking garages in downtown areas takes up high-value land with a massive, noisy, dirty, eyesore. In fact, some research has shown a negative correlation between the percentage of downtown area covered by parking and the amount of economic activity in them (though, this research does not establish causality--there is an extent to which parking is more likely to be added in already declining neighborhoods). This suggests that simply adding more and more parking may not produce the desired effect--the benefits of increasing the ease with which customers can reach downtown businesses must be balanced with the cost of taking up valuable real estate and creating a business-hurting eyesore. The result is that we will probably never achieve a reality in which going downtown is as easy as going to a suburban shopping mall.
I would, however, caution people against arguing against the need for more parking on the basis that "I can always find a parking spot somewhere," or some variant of that argument. It is quite likely that downtown populations and business is constrained by the amount of parking, even if you can usually squeak by finding some parking spot on some forgotten side-street. The reason is that in the real world people do avoid downtown areas because of the difficulty and cost of finding parking, with the result that many downtown areas never grow enough to completely use up the available parking. That is, you found parking downtown not because there is enough parking, but because some suburban commuter decided that there was too little parking to try to go downtown.