The other thing of note is that Steamboat Willie and indeed Mickey Mouse are complete shit - did anyone ever watch these as a kid? When I was a kid, there wasn't that much "media" around to "consume", and even still this utter shit didn't make it to air.
I seriously doubt anyone will ever make any more money out of Steamboat Willie - ever (not even Disney). Digitally remastered Bluray? You've gotta be kidding. Even a Youtube of it would only get views in the first couple of months as people wondered what all the bunfight's been about for all these years.
As for Mickey - as you say he's trademarked, so that's a different ball game entirely. They can continue to use those ears and whatnot exclusively without any new laws to help them.