Got my reissues today. It's been a great night digging through the bonus discs and I'm still getting properly acquainted. Some of the unreleased songs are just sketches or curiosities, while others are genuinely great tracks like "Convent Girls", "Spirit of the Stairs", "Tail of a Comet", "Anthem", etc. Right now I'm enjoying a tune called "I Don't Know You". As for the early/alt versions of songs we know, again some are sketches while others are fascinating, like the Zen Mix of "Locked Out". And apart from the three title words, there's nothing in the original "Whispers and Moans" that sounds anything like the song we know! It's a totally different song.
Also, the version of "Can't Carry On" on the regular album has an - unadvertised - extended ending! The fade-out is later. It's great.