Well, the way it seems to be working now, you have a better chance of getting the stuff you're looking for from the old packs is by buying the new ones. Those grand chance cubs are plentiful and are always looking to give out old stuff rather than the new stuff.
That being said, in the current condition, if they were to bring back old packs for sale, you'd be getting stuff from other packs you don't want, instead of stuff from the pack you're buying from. Just like the way it works now.