Even if you go to Beaches and Cream and Pepper Market - where it is nearly impossible not to spend more than you'd pay for a voucher, it may not be worthwhile if you wouldn't go to those places anyway. Neither is convienent to get to from the mainstream parks, and when we do Disney, time is more valuable to us than a few bucks. But other people place less value on time and more on money - and if Beaches and Cream and Pepper Market are on your "must do" list - or you have time to spare for the trip - or you are staying at CSR or the Y&BC anyway, the vouchers are a great value at these places. (B&C is on a lot of people's must do lists without vouchers).
Steve, I'll have to disagree with your "obviously." Although I'm not a voucher person, a lot of people here like having their meals pre-paid - even if they don't save money. As we have discussed before, money and budgeting is not just about math - its also about emotions. If pre-paying meals makes people feel better - or makes them better at managing their expenses - or keeps them from overspending while at Disney - more power to them.
You and I are pretty much polar opposites in spending and food at Disney - we love our sit down dinners and regularly spend $40 per person on dinner and drinks each evening. But because of the style in which we eat (a big sit down dinner - but a light lunch without dessert, no desire to share, and I usually skip fries and pop), vouchers don't make sense for us either. My kids are little yet, and I hope they are responsible enough that when the time comes to let them go off on their own I can hand them a $20 (or even give them room charging privledges) and know they will eat and not break the bank. But who knows what the future holds....I can see the benefit of spending $11.50 to know my kid had no excuse not to eat lunch (because he spent his $20 on Dole Whips and arcade games) - even if he only buys $6 worth of food with it. Worth $6 in peace of mind. Your peace of mind may not be worth $6, but mine is.