From the Ask The Answer Man column in Adventure Comics #455 (1978):
I love you, Bob Rozakis, but this is so wrong!
Leaving aside all of the economic issues--sure, I know they couldn't continue to produce 100 pages monsters for 50¢ or 60¢--I'm really not sure you can say "contains no reprints" as a positive, and not a negative.
Nothing against new stories, but for a comics fan of the right age, those reprints were a godsend.
Recall, if you will, in that mid-70s era, these old stories were nowhere as nearly accessible as they are today. Comic shops certainly weren't as available to the majority of readers. There were no trade paperback collections or omnibi awaiting us in bookstores. There was no internet or Comixology, no place to legally (or even illegally) download gigabytes worth of old comics.
So for a lot of those older Silver Age stories, and especially the Golden Age tales, these 100 Page Spectaculars were literally the only source a couple of generations of comics fan had to access them, aside from the random garage sale or flea market.
My first exposure to Kid Eternity, and the Silent Knight, and the Star-Spangled Kid, and Superman Red/Superman Blue, and Wildcat, and Johnny Quick, and...well, let's just say that for me, and no doubt a lot of today's creators, our first exposure to a massive chunk of DC history came from the reprints in these humongous comics.
Marvel, of course, had a much shorter history. Yet during this era they had entire books dedicated to reprinting the early Silver Age stories of Spider-Man, the Fantastic Four, Thor, Iron Man, Captain America, the Avengers, etc. Meanwhile, aside from the reprints in the 100 Page Spectaculars (and a few other similar projects), DC showed little interest in sharing its past.
So, yeah, yay for Dollar Comics. But boo for no reprints!!