When I was on DDP, I felt "locked-in" and never wanted to order any food off the plan, because I was pre-paid. With TIW, I feel better eating off-plan (like a Giordano's pizza delivery or getting a snack from a BWV vendor)
As far as savings, the DDP works well if you would normally get ADR's at expensive dinner options (i.e. LeCellier) Otherwise DDP is simply a pre-paid dining plan (not a discounted dining option)
But You can fairly easily dine for less than DDP cost if you are willing to only do a TS breakfast or Lunch, or stick to ~$20 dinner entrees. a Chef Mickey's breakfast can kill the value you just got on a LeCellier dinner...
TIW savings can quickly add-up if you typically buy alcohol and/or appetizers(included on TiW), and TiW discount can be applied to everyone (up to 10) at your table, nice if you meet with any family or friends
You have to look at what you would pay total OOP. (including appetizer, alcohol). 2 trips ago, it seemed that our total room charges were adding up too fast, then we did the math on DDP + appetizer and realized we came out $100-$200 ahead with TiW..