I have not used vouchers myself, having decided that the way we travel any money they would save us wouldn't be worth the bother (to us)....but...
For your meal at Boma, you'd need a voucher for a sit down dinner. I'm not sure what the price is on these vouchers, but I seem to recall that they are in the $60 range. And you'll need one per adult. Since the Boma buffet is less than $25 per person (plus beverage, tax and tip) and vouchers don't include alcohol, you'd need to be an awfully big tipper to make a voucher worth while for that meal.
For your SciFi meal, you'll need a VKL (Vacation Kingdom Lunch) voucher - at $30.50 or so. This should get you three courses and a beverage (I'd recommend either splitting or making this your big meal of the day). Ordering the most expensive stuff - Onion Rings are $7, an $18 steak, a $5 dessert, a $2 beverage and you are looking at a $32.00 meal - before tax and tip. Ordering the lowest price stuff on the menu - a $4 salad, and $11 burger, and dessert and will still set you back around $5 and $2 - you are looking at $22.00. Add tax and tip and you will about break even. Skip a course and just get a burger, and you'd be better off paying cash.
For counter service meals, you want the Q&C vouchers - $11.25. A good deal if you will order extra fries and dessert - or if you are planning on going a little out of your way to eat at Pepper Market or Beaches and Cream - where these things will save you again what they cost you. Do keep in mind that Beaches and Cream and Pepper Market are both a little out of the way, unless you are staying at Y&BC or CSR respectively. Once again, if you eat an extra side of fries and a dessert (or split - to make one burger and an extra side of fries and a dessert feed two), this will save you money. If you are like us and never split and skip the fries completely that come with the burger (saving about $1 on the meal - plus all those carbs), and never eat dessert (more carbs, more money - and I'd rather save my empty calories for the really good stuff), you won't save money.
If you are planning on a character breakfast, those vouchers are $17.75 for an adult and $11.00 for a child. Chef Mickey's will set you back $17.00 for an adult and $9.00 for a child before your add tax or tip - so its pretty impossible to lose money on an adult character breakfast voucher, and you'll at least break even (or close) on the kids - unless you end up not using it.
I'd pick up (well, I wouldn't - I'm not a voucher person, but...) one VKL for each adult in your party for Sci Fi, and one Q&C voucher for each adult in your party for the two days you are in the park but not going to the Sci-Fi for lunch. I might not (YMMV) get Q&C vouchers for the day you dine at Boma (since that is an all you can eat meal, and you'll want to bring an appitite), or get only one and plan on splitting that lunch.
