Wow, amazing story. Yep , there's magic in those old LPs!
I have a few comments from a Dream Theater fans perspective, I hope they're helpful!
Crosby, Stills & Nash - CSN
A moody and mature album. Although the name suggests a debut, this self-titled album was later in their career. Not proggy, but more intricate than their folksy early stuff. Highlights for me are Shadow Captain and Cathedral, and maybe Dark Star.
David Bowie - Hunky Dory
Bowie in his prime, IMHO. Easily as good as his Ziggy Stardust album. Guest piano player is Rick Wakeman from Yes. Light-hearted (Kooks), heart-felt (Quicksand) and bizarre (Andy Warhol).
Grand Funk Railroad - Grand Funk
The only Grand Funk album I ever got into. As heavy as it gets. Last three songs (Winter in my Soul, Paranoid, and Inside Looking Out) are just classic. Sounds almost recorded live in the studio, too.
Jethro Tull - Thick as a Brick
A prog-rock masterpiece. One 40-something minute song (like 6DOIT). Takes about 10 listens to "get it", then you'll freak out at the melodies, lyrics and transitions. Start of 2nd side is maybe just too weird, but when they bring it all home at the end... what a payoff! If you have the version of the LP with the full newspaper inside it, you're in for an entertaining read while you listen.
King Crimson - In the Court of the Crimson King
This album is to prog-rock is what Black Sabbath's debut was to metal. 21st Century Schitzoid Man is as frantic and cool as it gets. I Talk to the Wind is typical 60's music, but made really tastefully. In the Court of the Crimson King is a case study in trippy lyrics. Also has Greg Lake before ELP.
Yes - Close to the Edge
Yes - Fragile
Yes - Relayer
This music, to me, is Dream Theater without the metal. Fragile's South Side of the Sky and Heart of the Sunrise will shock you, if you haven't heard them. Some true prog epics on par with Octavarium, Change of Seasons, and 2112 (Rush). Not catchy... takes a bit of work, but just amazing especially considering the old, analog equipment they must have used in the studio. Like Floyd's Dark Side of the Moon, these albums were crafted with care.