Just to clarify a couple of things:

1. There are many reasons for copyright, economic incentive is just one of them. It can, as an example, be used to restrict the distribution of a work. (Copyright applies to almost everything, even if it isn't published.)
2. Public domain works were certainly available in the past. Certain publishers seemed to specialize in printing public domain works. Project Gutenberg has been around for about 30 years.
3. Copyright laws are usually made stronger when copying becomes easier. This may sound contradictory, but it makes some sense because a market would still exist after the copyright expired when copying was hard.

I'm not entirely sure where I stand on long copyright terms, but I am disgusted by retroactive copyright extensions. Not only does it introduce unpredictability in industries that depend upon the public domain, but it completely contradicts the most commonly cited purpose of copyright laws: the incentive to create new works. As the Green Party implied, 20 years provides incentive to create a new work. Over 20 years provides an economic disincentive to create new works (since you can live off of the old).

One idea that I find appealing are fee based copyright extensions: free for the first 20 years, $100,000 (or whatever, and inflation adjusted) for each 10 years thereafter. This solves the problem of abandoned works because it automatically enters the public domain in a reasonable time frame if no one can prove ownership over it. It provides economic incentives for "great works", i.e. anything of lasting value. It also ensure that a work can still serve the public good even if the economic incentive to publish it no longer exists.

Finally, I don't think the idea of private copying (which is different from non-profits copying) would work any more. Simply put, copying has become too easy. But I do think that private copying should be treated more like tickets: small and reasonable fines based upon the offence rather than mostly arbitrary court rulings.