I have Led Zep at the Madison Sq. Gdn (circa '73) and was VERY disappointed with the PQ. I expected a proper HD pic from a clean transfer. What you get is more Super-8 quality. Soundwise it's fine I suppose, although can't really tell as I wouldn't call my system a home-cinema set-up.
I'd have been surprised if the PQ was all that on a concert filmed 36 years ago, to be honest. Gigs are not the easiest things to film evan today and I doubt there was anything capable of practically recording a gig from multiple angles in HD-quality back then, the older films that have been remastered well were filmed on huge cameras with analogue film.
Personally as far as gigs go I'd take a rough picture so long as the sound has been done well.