Cap'n Bulldozer -- I'd never thought about the Class decks and hadn't really dug into those. In fact, I can't even say that I have a good idea what's in those boxes. It didn't make sense to me considering that the B+C boxes already came with 11 characters and probably 300(?) cards worth of items, weapons, armors, etc. It never occurred to me to even consider a Class deck. Can you tell me more about this?
In short, the class decks (and ultimate add on decks) were originally designed to supplement organized play. They each consist of a few new characters, as well as around 100 boons that, at least theoretically, complement the characters in the box. There's one for each of the Pathfinder classes; Monk, Paladin, Druid, etc. as well a few that introduce completely new classes (some even with primarily Goblin based stuff). The decks themselves are relatively inexpensive, figure 10 to 20 bucks for one (though you can sometimes find them for much less).
The thing is, quite a few of the cards in those class decks are totally new cards that aren't found in any of the Adventure paths. Some of them are repeats as well, but it would mean you could use them to have access to cards from outside the AP. At least some of the cards are quite good as well.
(You can check out https://pacg.fandom.com/wiki/Pathfinder_Adventure_Card_Game_Wiki
for deck lists and text of the cards, etc.)
I personally never got into organized play, but I still have picked up almost all the class decks, and will select a few specific cards to add when playing, both for some new "rare" cards and also sometimes to adjust the difficulty, or to compensate for the AP card selection being not to my liking. Some people prefer to add in the entire class deck, but I found that clutters up the box too much most of the time, and tends to add a bunch of cards you don't really want in there from time to time.
As a bit of a warning, the cards you add can affect your play experience in some strong ways. For example, when I recently played through S&S with the S&S version of Lini, we added a toad ally from a class deck, as well as some mastiffs. Toad let that Lini get spells back from her discard pile easily every turn, while the mastiffs essentially let her draw 2-4 extra cards a turn. That meant she was usually playing 2 divine favor spells a turn and still having a ton of other action. The class decks are not balanced around the APs, so you might want to carefully consider what you add if anything. (In my case I was playing with my 9 year old son, so we didn't care too much about having uber powered Lini or Mother Myrtle, but some would find that less fun obviously)