Buying an upgrade onboard would depend on if there are rooms available. I have not done it but have heard of people doing it on Carnival.
Yes I do believe Carnival has a wine package.
The soda card was $34.99 for a 7 day cruise on Carnival and it is a seperate card not a sticker. It does include the tips.
I have never had a bad meal on Carnival. I have had good to exceptional but no bad meals. I felt the choices were limited but I have never had a bad meal on Carnival.
If the port is Casa DaCampo or Laramoana, both dock in the same place, we found the artist colony in Laramoana very beautiful and quite interesting. We did not go anywhere else while there.