I used the breakfast vouchers on our last trip. I paid $17.50 (I think) at the time.
The princess breakfasts each cost $19.99 per adult, $9.99 child.
So I figure 19.99 + $1.75 tax (I used 8.75% which is what it is here in Chicago) + $3 tip. That's a total of $24.74. Even if the tax in Florida is cheaper, you get the idea that you save more than $4 on these breakfasts. When you multiply that by 3 people (my DD is 12 so counts as adult), you save more than $12 on the meal. Plus we went to both the Cinderella breakfast and the Princess one.
For the cheaper character breakfasts (Like Crystal Palace at $16.99), you save around $3 per adult or the cost of the tip.
The kids vouchers seem to be about breakeven. I usually just pay cash for my younger DD.
Maggie