Aside from the Hunter cards, I never disenchant adventure cards. Because the only way to get them back is by crafting them again, which costs far more dust than you got for disenchanting them, and you never know when even one that looks bad might get a new card printed that makes it more playable, because Blizzard designs things to do that intentionally.
Which is utterly irrelevant. The point is the impact that it has on the game's overall economy for a player who is mostly (not entirely, mind you, I do spend a small amount every second expansion) relying on gold for his cards. A month worth of gold is a full quarter of the time we have with any given expansion - one-quarter of the packs that I'd otherwise buy from an expansion that I won't get if I buy the mid-expansion adventure. That's a lot of cards lost, for the sake of a bunch of cards that, previously, wouldn't have existed at all. Dust value is completely meaningless in the face of that - this will make it harder for me to collect all of the cards I want over time and make it more costly to keep up with the meta, and that is just a hard fact. That's how it works when you add more expenses to the game's economy but leave the amount of gold the same: there's less gold for the things you were spending it on previously. That's just basic math.
*double-checks this* ...okay, wow, I must admit that genuinely shocks me. When I looked over that announcement earlier, I skipped straight to the cost and the information about the new cards, because I've known I would have this problem with it ever since they indicated it would have new cards back when Descent of Dragons launched, and wanted to see if there was any surprises there. I fully assumed it would just be more Dungeon Run, since that's been the only kind of single-player they've done for so long (aside from Boom Labratories' puzzles, which I personally liked a lot more than Dungeon Run, but seems to have been a one-off), and I was not expecting a change in that regard. Admittedly, it is nice to see that this will be more like the old adventures and not just another Dungeon Run variant. Still, that doesn't excite me or anything, and certainly doesn't make up for the core problem of introducing a new set of cards in between expansions and charging for it like this.
There is little more rational than mathematics, which is the basis of my complaint. Again, more things to spend gold on, but no more gold to spend on them, equals less gold to spend on what we were already getting before anyway. Which means it's harder to collect everything you might want. And frankly, they've been making the game harder to play casually for a long time now, between switching from the expansion-adventure-expansion cycle to all expansions and the nerfs to the Classic set causing decks to rely ever more on expansion cards over time. This is just the straw that's finally breaking the camel's back there for me.