Hi Kat, Welcome to Cruise-Chat!
I haven't sailed on Disney so I can't make a comparison. The "Fountain Fun Pass" (soda card) is a little on the expensive side. I am pretty sure these are the current prices;
Adults $6.33 per day X length of cruise.
18 and under $4.60 per day X length of cruise.
Those prices are inclusive of the 15% gratuity.
As far as the Carnival Miracle goes I have sailed on two of her sister ships and loved them. They are laid out very well with deck space and passenger flow.
Good luck, and welcome aboard,