A bit like in the programming area there is a Code Snippets board in which people post their souces and others learn from.
If this board was set up, I for one would post all of my PSDs (however rubbish they may be) and hopefully it will turn to a trend and many others will follow. Every PSD that is made has the potential to teach someone something.
Obviously the downside to this idea is ripping of other people's work so strict rules will have to be enforced and perhaps normal members will have to meet some requirements to view.
As I said I am against paying for PSDs but an alternative method to the above could be to set up a trading board where we exchange PSDs for PSDs, not any form of credit or money. This could be used for all those members who feel strongly about their work being ripped or do not want to make their PSD completely public.