If i dust cards that i get from like.. naxx or old expacs can i craft them later

yes but you'll have to pay 4 times the dust if you want to recraft them

Word thanks mang

Unless if you plan on quitting and don't care, it's a very bad idea to dust non duplicate cards.

Dust everything for like 20 golden tinyfins, pussy.

No real point since you can only obtain them once unless you crafted the golden version.

Cards that have no use can be dusted 100%

If you don't play wild, dust your wild cards

they are also useful for tavern brawl.

and have you ever considered the possibility of blizzard introducing new game modes in the future ? these cards could be important.

I have and the majority will only play whatever blizzard wants you to play

Which is standard

I dusted my naxx shit. Got like 2 legs worth of dust, no regrets.