Depends on your individual situation if it is better to keep unlimited or go with Share Everything. Normally,the plan I'm on, two smartphones, 1400 minutes, u/l text, u/l data would cost $200/mo w/ taxes and fees. I get $20 off each unlimited plan, bringing total to $160.
I don't use enough data to justify holding on to unlimited at any cost. We have never gone over 1GB total any month in the year and a half that we had smartphones. So Share Everything, two smartphones cost $80, 2 GB cost $60, taxes/fees $20 = $160.
Given that we like to get a new phone as soon as eligible for a subsidized upgrade, every 20 months, the total subsidy on two top of the line phones is $900 every 20 months, or effectively $45 every month. That's too big a discount to forfeit in order to hold on to something we really don't need.
If you use a lot of data, it may be worth paying full price for a new phone to keep your unlimited plan. You are paying extra ( from my perspective) in the loss of your subsidy.