[ZeroGFrame]

Well, the in-game cards add a lot more than the Background cards do. I don't remember how they did it in Masterbook (I remember them being a cool addition, but not really necessary, as you said), but in HDL the cards can be turned in for Experience, which can help in a lot of situations (especially since the system is bult around spending experience for things other than character improvement), and are just useful in general. I'd suggest you at least give the cards a try, and see what you think, rather than just writing them off.

Here are some examples of cards:

Bonus: gain +2 to a single roll
I'm Glad I brought This Shotgun: get a weapon if you don't have one (or turn in for 2 EXP)
Failure: Opponent fails a roll (VERY useful, and has saved my players on more than one occasion), or turn in for 2 EXP
Wait For Me!: you go first
Retry: re-roll a check (instead of spending the experience to do it)
Sacrifice: get 5 experience if you risk yourself to save someone else
Extra Action: immediately take another action (useful in an action-based system, especially if you're outnumbered)

And these are just a few... there are many useful ones. Anyway, just my two cents.