As for the old & new deck, this is what I've seen:
"The damage deck included in this box replaces the damage deck in the original X-wing core set. If players have both, they should use the new deck included in this box"
So, if the new deck really is considered better than the old one, and since your own deck is always used against yourself, doesn't that mean it's to a players advantage to just not have the new deck?
Yes and no depending on your squad. People running Elite Pilot Upgrades/Named Pilots/Secondary Weapons will still not enjoy the old deck.
Everyone that wants to dish out ridiculous damage (really just everyone) will enjoy this new deck.
Crit damage got a significant boost with this. Time to break out the Mangler/ATC/Calculation/Mercenary Copilot/Marskmanship(hah just kidding on that one)/Etahn Abaht.