I'm a lacto-ovo vegetarian (eggs and dairy okay, no meat, poultry or seafood) who did 10 days on the
DDP last year, and I agree that the DDP is not as big a financial windfall for vegetarians as it for the carnivores. But it's still a good deal, IMHO.
For example, one of my favorite meals was at R & C. I had a fruit and cheese plate: $9; vegetarian entree: $13; and the sticky toffee pudding: $5. So far, only $27, but then you factor in the soft drink and tea they included (can't remember the prices, but let's be conservative and say $5 for those) and now we're up to $32 ($40 after tax and tip). Toss in a CS meal from CHH (1/2 sand & soup, soda & cake + tax =~ $13) and a dole whip float ($4), and my total for the day was 2 pounds. I mean, $57 (I don't do that other equation until after I get home

). So the savings was only $18. Like you said, not as great a deal, but still a deal.
Could I save a little more by skipping the DDP? Yes, if I order less food, but the real savings to me with the DDP is in knowing that everything is already prepaid, I won't come home to any big bills (except the one I can only pay off on the treadmill), and I can enjoy the indulgence of having appetizers, desserts and snacks, since it's the same price either way.