Everything not yet leaked would be fascinating to read. Even Darabont's earlier drafts (we have #3) would have potentially been different enough to be of great interest. Aren't his earlier efforts rumored to include Indy's daughter and a heavier Nazi presence?
I'd also love to see Lucas' revision of Darabont's draft because it would articulate what exactly he didn't like about Darabont's work.
Remember, we still don't have any of Jeffrey Boam's work, either, only Jeb Stuart's. Lucas was not satisfied with the saucerman concept until Boam's last draft. For all we know, that's the one that actually makes a decent case for Lucas's idea.
As far as the date...I don't think it would have changed much, at least not implicitly. I think any year after Roswell would have functioned about the same. It's clear that the only significance of 1957 specifically is that it's 19 years after 1938. It's also much easier to sell the age of Harrison Ford if it's closer to the truth.