"I love playing vinyl on my 70’s classic rock albums"
The album producer had a big part in the SQ of your Classic Rock album too.
Ted Templeman is an example someone responsible for great sounding LP’s in the 70’s
A few examples
"But I’m curious about how much difference vinyl makes on older albums that may have not had the best recording techniques"
Play a period press of your favorites on a proper setup and your perspective may change?
As mentioned, some of the arguably BEST sounding LP’s are 50-60’s original pressings-you just have to hunt for those unmolested copies.
Just like a broken record, I’ve mentioned this LP many times being one of those recordings that may change your mind about how good an old record can sound
1955 mono recording-the real deal
Likely, not a genre most of the younger generations would listen to, but if you’re interested in listening to musicans/vocals of "days gone by" this an example of greatness.