The 48.75 voucher for Breakfast In the Park is just that, for breakfast and can be used at the locations stated on the voucher.
They are: Club buzz at Tomorrowland and Pacific Wharf Cafe at DCA. If
Disneyland opens at 10:00 a.m., you can use the voucher at Carnation Cafe ONLY if Disneyland opens at 10;00 a.m.
All other food outlets are under NO obligation to accept the voucher.
A recent memo went out stating that fact that vouchers issued as part of a package are to be used at the location(s) printed on the vouchers.
Once exception, if you have a mult-day meal plan with dollar-denominated vouchers, those can be used at any location that serves food.
If you're going to upgrade to a Character Meal, just take your voucher into the Disney Travel office in Downtown Disney and they will be happy to give you $8.75 credit and apply toward the cost of a Character Meal.
The Character Meal vouchers are great as they include tax and tip!