Same here. Have all cards: NR, Skellige, Monsters, NG. Have most neutral cards. Have all SC bronzes ( just in case ), milled all golds and silvers cause i dont like this faction and never will be playing it. So i started to hoard some time ago. By the time new cards will be out i should be able to craft all of them day one. Only 20 of em.
I would say that you should open kegs when you get them simply because you'll get a better rank reward at the end, don't dust anything at all because sometimes you can capitalise on full refunds given. Potentially save your ore however if you have the best meta deck or a deck you think is optimal and doesn't require any more cards. That and try not to spend scraps because if the kegs just going to get bigger and bigger will increase rng on gaining that new card. I'm personally waiting to see if there will be anything more than the initial keg, like expansion kegs, if that was the case I'd just have fun with scraps to a point where you still are saving some.
the moderator was not wrong about the kegs being set. I think this is a Mechanic to protect against disconnecting as you can still pick a card from a keg. So if you have any kegs that you have bought saved up then it is pointless, but is judgement based call on how much ore you save. If you're free to play obviously every scrap is precious.