We did a family trip with my wife's sister and her fam including my MIL and g'ma. It was a blast. 10 people...my oldest was just 2.5 at the time and my wife's gram was 80...that big of an age range and we all had so much fun!
We said... "Maybe every 3 years"...then "every two"..."Every other"...

As you can see in my sig, we were there in march and again 2 weeks ago!
Once we met with the DVC folks and saw the rooms...my wife and I both knew we wanted it without even saying a word to each other!
The rule of thumb is 6 trips and you're at break even. My fiscally conservative Certified Financial Planner whom I sometime call my older brother...was the one that assuaged my fears and convinced me to join.
As for the Disney Visa...we use it for everything that allows cc payments. Then we just pay it each month. We upgraded to the premier one this year, too. The annual cost was nothing given how many points we earn in the course of a year.