Looking at the posted prices, 2 credits doesn't seem that far out of whack.
Tier 1
Seating 1 - $32.99 plus tax & gratuity / ages 3-9 $17.99 (Lunch)
Seating 2 & 3 -$44.99 plus tax & gratuity / ages 3-9 $22.99 (Dinner)
Tier 2
Seating 1 - $38.99 plus tax & gratuity / ages 3-9 $12.99 (Lunch)
Seating 2 & 3 - $44.99 plus tax & gratuity / ages 3-9 $14.99 (Dinner)
Tier 3
Seating 1 - $51.99 plus tax & gratuity /ages 3-9 $13.99
Seating 2 & 3 - $59.99 plus tax & gratuity / ages 3-9 $15.99 (Dinner)
It may not be worth while at the Tier 1/2 restaurants, but the Tier 3 restaurants thats pretty much the cost of 2 regular TS dinners. Typically about $30, correct? And glancing at the Jiko menu, (which I believe is Signature dining, also 2 credits) its about 11 for app, 36 for entree, and 8 for desert, which is pretty much the same price as the Tier 3 dinner pricings, if not less. Narcossee's looks to be a bit more, but they probably all balance out.
But once again, Disney knows its about convenience. Where the DDP is so popular, many people don't look at the actual cost involved, and just do it. Just like using a room charge or plastic chips at a casino, the DDP helps to have people consume something without really thinking about the real cost to them, since they don't "see" the bill for the actual meal.