Actually my first Ektelon was a D which I got used from a sporting goods shop that was closing--and that was in the mid-70s. My first H was in the mid 80s--85 or 86 I believe.
I am not sure that vintage machines have much value as collectibles but maybe a Serrano (or one from the article I note below) might be an interesting conversation piece in a study with an antique racquet mounted in it. But you need both the room and an understanding spouse.
You might want to check out this article: