Basically, I think you should buy this because if you haven't heard 'Seconds out' on LP (vinyl), then you haven't lived. The CD version has always been (and still is) plain awful. The original LP release exhibited everything that was great about Phil Collins' drumming, in the context of Genesis too. I cannot stress enough, that if you like 70's Genesis, and haven't heard that LP version, then you MUST hear this new DVD version (with DTS), because it's simply the best of the best!
I NEVER get bored listening to this era Genesis, never, ever. So, to worry about what is, or isn't included in this boxset seems trivial. All the DVD versions sound great, and they bring to fruition what Genesis truly were - a fantastic band that sounded best, live! The 5 songs from 'The Lamb' are especially interesting, because, unlike the original album, they sound MORTAL.
It IS alot of money. It took me 2 years to decide. Now that I have it, I simply wonder WHY I delayed. 'Firth of fifth', 'The cinema show' and 'Los Endos' when sounding as they truly should, represent the very, very best of Genesis live. If you've not heard these properly, then I can't emphasise enough, YOU MUST! Utterly essential.
As a postscript, there is a danger that the 5.1 SURROUND SOUND again makes the music sound like easy listening. The reason it does this, is because it brings forward the bass primarily (the playing of which is fantastic, I should say), and as a result it 'smoothes' the sound somewhat. I don't have surround sound, and I hear the DVD's on headphones. It is on these that the balance is more towards the drums (thankfully). I'd hate for you to be mislead by my comments. It may be that the best experience is available only through headphones. Even so, it remains a fantastic experience.