How do I use cards/Will they help my DPS a lot?

[Zeryph]

"DPS just increased hugely, thanks cards!"
"I don't want to be offline without my card gains"

All this stuff... Is it true? Do cards really boost DPS that much that it's worth it? I have some questions to ask.

First of all, cards. Can I do it at my level 81? I've opened the card packs from the support packages before and gotten 5 cards for an enemy, and with my 230 cards total I have +46 base damage. Compared to my 2,600 DPS I don't see how it's helping so far. Should I try and farm cards? And do low levels where I can one hit enemies also drop cards at the same rate as hard enemies, but still give the same Base Damage bonus? Because if so, I'm going to farm loads of cards from enemies I one hit kill.

Second, is this "card DPS bonus" for only people who reached Inferno?

And finally, should I begin farming cards at level 81? Is it really worth it? Would it help me quickly improve my 2,600 DPS? Because right now I feel a bit weak at AT2, and it would really help me if I could and it was possible.

Thanks for putting up with my endless questions!