The DDE is not a 'one size fits all' type of perk. For 2 people, it only works if you go often enough, and dine enough, to recoup the cost of the buying the DDE card.
If you're a larger group, then you may recoup the cost of the card with just a couple of meals. Especially if you purchase alcoholic beverages.
I don't see a problem with the automatic gratuity except that it is mandated. We would tip that amount anyway, but if making it automatic winds up lowering service, then it's a bad thing.
As for the card, I think it's still $65 to purchase. This would put the break even point at $325 (20% off of $325 = $65), so if you know you'll be spending at least that amount in all your visits (one visit or multiple visits) over the course of a year, then it would be a benefit. And remember, that's $325 at restaurants that accept the card. Not all restaurants do.
And a couple of other things: 1. We already get a DVC discount at a number of restaurants. If you eat somewhere that accepts both the DVC discount and the DDE discount, then by having the DDE card you're really only gaining the difference between the two discounts. Thus if DVC were 10% and DDE is 20%, that meal you only recouped 10% toward paying for the card.
2. The DDE card is not good at CS restaurants. The one exception now is AK because they don't have a TS restaurant yet. But as soon as the new one (I forget the name) opens this December, my guess is that the DDE card will no longer be valid at the AK CS restaurants.