i just started too
think the cards are not that great,
coz once the card activate, ur party need to do damage on that turn,
unless u have that earth/water dwarf,
he has that skill to attack right after a member hit.
then that buff and increased crit will be ok...
overall, like what cloudst said, claim and combine 4* to 5* is better...
but i prefer get the powder rather than go for the cards.
there is also an event where they will reward you for having 4-6* cards,
how and when they reward need clarification though