If you are paying $250 (subsidized) for 4 lines (3 smart and one flip with mobile share plus one iPad for 6gb
You should seriously consider the $100 10gb mobile share plus $15/line (no subsidy) plans.
$100 x 4 lines equals $160 plus $10 for iPad. So $170. Plus taxes minus 25% discount off the $100/10gb. So $75 plus $60 plus $10. So $140 plus taxes. Comes out to around $160 total for your plan. That's with no subsidy.
Considering the subsidy is worth around $18.75-20 a month max. It may be worth it to switch (if you didn't sign any new contracts prior to Feb 2014 cut off date.
My brother upgraded in September, so that's a no go for us. I'm still in contract through this coming January as well, and I'm not sure when my dad's 4S goes off (it might be already, but he didn't upgrade at launch). Plus my parents would probably say that we don't need 10gb when 6gb is enough. My mom uses her iPad mostly on wifi at home, and I try to use wifi at home and school. I'd hope my dad and brother do too.
We switched to a share everything from the old style nationwide family plan in 2012 before they offered the discounts for getting more data. The store rep suggested 6gb based on three 3G phones and adding the iPad 4th gen. I'm the only one with an LTE iPhone 5, and of course I went over the first few months before I started using wifi. But they expected me to use less data instead of paying for more. I don't pay for it, so I don't argue.