This has been discussed here a few times before - you might want to try a search.
But, basically - I think many
DVC members have kept their Disney Club Cards for the discount you receive on multi-day passes. DVC members get a discount on length-of-stay passes, only. Depending on the size of your family - the discount you get on passes could pay for the card, itself.
Also - unless something has changed - your DVC membership will get you a discount at the
Disney store, only, while the DC card will get you a discount at the Disney Store Online, as well as the catalogues.
The discount at the stores on Downtown Disney differs a little, also, but they recently changed the DVC discount, and I'm not sure I recall the exact differences, now.
You can view the current benefits on the DVC website, and also view the current DC benefits on the Disney website for more information.
I struggle with the justification each year at renewal time, also - but end up getting it again every time...