Honestly, I think we just need fo go back to life+75 or something that covers the next generation.
Copyright is a fairly basic protection on Work, and wanting to alter it to be based on percived value is catastrophic- On one end you'll deny copyright to security camera footage- nevermind it's of a meteorite and everybody is clamoring for a copy. Then, on the other hand you'll have micky mouse where it's such a big thing and Walt put so much effort into it that the copyright is perpetual. It'll tie up the courts, and give the Have's the power to remove the copyright or SLAPP the rightsholder into poverty.
We need patent reform far more than any complaint against Copyright that I've seen- and far too many people conflate the two. Lets not even talk about trademarks.