The fact that copyright is longer than patents makes no sense. Patents prove that a shorter period is sufficient to stimulate large investment. And you have to pay for patents!
If you assume reasonable discount rates, the economic value plummets over time for an asset producing the same income (a bad assumption for copyright work in general).
At an 8% discount rate, extending copyright from 32 years to infinity adds less than 10% to its total present-day value. There are many good reform proposals, but mine would be something like 15ish years of free copyright, followed by 1 paid renewal for 15 years that is modest in price (eg $1000) and one extra 10 year renewal that is something like $1M. Meaning you have most economically neutral work free up at year 15, small business types having it affordable through 30 years, and the big Hollywood productions can go from 30-40 years for a modest (to them) fee to incentivize investments in expensive works. Movies come to mind. Give existing work a 20 year buffer on top of that to transition and there is a very small economic effect on everyone.