Excluding work-for-hire, does a copyright transfer affect the copyright term in a way that makes the date of the original author's death no longer relevant? (IANAL and couldn't find a discussion of this when I had a quick look.)
Ignoring the impact of author death still doesn't change my original question of whether a longer term "significantly benefits everyone else making a living off intellectual property" and society in general.
This isn't complicated. A copyright is worth more if it lasts longer. An author can sell her rights to a work for more money if copyright is going to protect that work for a longer period of time. People making a living off intellectual property can be expected to make a better living in a world in which copyrighted works have more economic value.
The stuff about death + N is an attempt to tie things to an intuition of moral rights; the business case is actually pretty poor in general. The net present values of an asset leased for (say) 30 years, versus 130 years, are surprisingly close in value, not least because of the uncertainty in predicting the future.
Ignoring the impact of author death still doesn't change my original question of whether a longer term "significantly benefits everyone else making a living off intellectual property" and society in general.