Basically, a record collection that was built during the 70s would be very different from a collection that is built about the 70s. A person today, setting out to collect "the 70s" would have a solid list of great albums to collect, in a host of genres. But a person living through the 70s would have a hodge podge of albums and singles - many of them still popular today, but many others that fall into that grey area of bands that never quite made it.
I think a really good example is Starcastle. They've got a great sound. Listening to it, I think maybe they were trying to take the sounds of prog rock and make it a little more accessible. The songs are a little more structured. When they were producing and touring, people loved them. Their records were pretty popular. But I'm pretty sure you're not going to hear a Starcastle song on the radio very often.
Another interesting band from the 70s was Hawkwind, who I think was entirely inspired by the scifi/fantasy works of Michael Moorcock. I'm just going to throw that out there. Warrior On the Edge Of Time is pretty good, and to me it feels like a cross between Led Zeppelin and Jethro Tull. Because of the flutes.