There are a lot of cards from that era that have had their prices driven upward. I blame Jerry's Nugget decks. There's that one run of souvenir decks from 1970 that used to sell for 50ยข in their gift shop and now trade for over $300.
Magicians started using them in their acts because they handled well and they were cheap (though even they joked about how ugly they were, in garish red and blue colors with the casino's derrick logo). Some of those magicians used them in their training videos, so they became "famous." Magicians wanted them, then collectors, followed soon thereafter by speculators - which drove the price up.
Now any deck even vaguely similar to the "J-Nuggs" has had the price forced upward by market forces, regardless of the true rarity. In fact, no one knows even how rare (or not rare!) the Jerry's Nugget decks really are, as there seems to be a LOT of them out there and that's not even counting the counterfeits that have been circulating (and getting better, unfortunately, though still nowhere near as good as the original).
So, would the value of this deck have risen on the same tide as the rest of the decks of that era? Likely. But $300+ high? That's some pretty deep water, and the deck's not USPC-made like the Jerry's were, so I'd be forced to say "Likely not that high." However, that's solely my opinion - others may feel differently.