If it were up to me, I'd balance the profit motive of the creator with the public domain value in the following way:
1. for every creative work that you'd like protected by a government-granted exclusive copyright, file a copyright registration form, sort of like a 1040 tax form. This registration gives you a one-year exclusive right, with no restrictions.
2. for years subsequent to the first year, you may apply to extend your copyright by filing another form. On this form, you show how much money you made from selling copies in the previous year. As long as this amount is more than 1% of the best year to date, you can maintain your exclusive copy right. If not, the work goes into the public domain.
So what would a rule like this accomplish?
For works like a book or movie or song, as long as the work was being actively marketed and bringing in a significant amount of money (more than 1% of the strongest year) you get to keep your monopoly right. But if you fail to get the work out into the market, free copying takes over as the distribution mechanism. Disney could no longer keep a movie in hiding for 10 years and then re-release it. They would be forced to continue marketing the work until they failed to rake in 1% of their best year. A newspaper or magazine article would go into the public domain unless the publisher sold enough reprints to keep it above 1% of the first year. Etc. The threshold value is defined by the best year. A hit movie might need to make $500k on DVD or rental royalties annually compared to its $50M initial release. A textbook might need to sell 10 copies per year compared to its first edition of 1000 copies. Etc.
This way, the public domain value is (I feel) appropriately balanced against the value to the author. This takes away the author's current ability to bury a work by neglecting the effort of distribution. Let the public take over when the benefit to the public exceeds the benefit to the author.
What do you think?