I hit millionaire just over 2 weeks ago and that's why I can now afford 12 packs. It's been great. I reckon you get to keep the card, but you can only perform the special mission for 10k starbits a day if you have 1 million starbits in your Hive engine wallet! I think it's definitely worth the sacrifice though.

12 packs are cool and all but you get loads of duplicates. Not a bad thing but scoring 6 unique cards out of 36 is pretty low.