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First of all, you are asking questions that are extremely subjective. Whether excursions or a drink plan is "worth it" is totally a decision only you can make. After 25 cruises, we are starting to enjoy having drink plans, but conversely, we do less and less ship's excursions, preferring to either do private excursions or simply do it ourselves (commonly called "DIY" here on Cruise Critic). But that is our personal view....it may not work for you at all.
Do you have access to a travel agent who is knowledgeable about cruising? That would be helpful.
Please look around Cruise Critic. There is a tremendous amount of knowledge and experience here. Every question you have has been discussed here....you can go through many discussions of points of view. You can't hurt anything by exploring widely on Cruise Critic.