I think we should also focus on works from the last 30 years and put some energy behind a copyright reform effort to get even older content liberated by legal means.
I'm sorry, but I believe this will have no measurable effect on the wiki.
In opposition to any effort this $100 million could possibly generate, the entire media industry is arrayed with a variety of well established lobby groups to ensure no such change takes place. It is resonable to suspect that the only changes to the law will be to increase the length of time for protections, while at the same time removing existing user rights.
I know its sad, but if you think that this money could change worldwide law that would end up having any real effect for the wiki, well, dream on. I understand your concerns about giving money to rich people, but let me assure you that it is precisely these people that would panic and dump (insert any sum here) into any effort to oppose such reform.
Meanwhile that same amount of money could liberate a huge variety of media that would immediately be available for use. Such examples would make the media holders happy, not mad, and could cause other media asset libraries to be put up for sale as well.
Maury