These are mixes that were put together by people that I admire and who really got me seriously interested in a career of recording and production and these mixes don't deserve to be "tinkered" with simply because we're living in a digital age or because an individual wants to put their personal touches onto them. These recordings are of a time and deserve to be treated with respect. By all means, sort out things like "drop outs" etc. but don't start changing the overall sound. If a listener goes home and thinks, "Well, I don't think there's enough bass or treble on this so I'm going to turn those up on my graphic equalizer." then by all means, but when I buy a box set containing music by a legendary group like the Beach Boys I expect to hear their mixes, no matter how bad some may be.
What if a song went unmixed? Or if only a reference mixdown was made with the intent of doing a proper mix later which never ended up happening?