A related question to ask which can contribute to the calculation on whether a drink package is worth it is: What are the occasions and venues on the ship that offer free drinks? For example, Captain's Club welcome party, Platinum and Elite welcome party? How many times do these occur (does it depend on the length of the cruise)?
Secondly, one can order the special drinks at the P&E lounge during happy hours on most days, at a discounted price ($8 / drink was the latest I heard).
Lastly, each person can bring one bottle of wine at time of embarkation to enjoy in the cabin.
I think these factors all can contribute to the calculation of whether or not to go for a drink package. IMHO.