Yes, the cruise lines do offer transfers for a fee. But most of the time they are considerably higher than doing your own thing. Plus, you have to wait until the bus fills up before you can leave. And you have to hassle with putting your suitcases in the luggage area under the bus, boarding with 45 people, getting off with 45 people, then trying to get your luggage from under the bus. Or you can hire a taxi for less money and do your own thing - quick and easy.
And as for NCL, you do have a choice with the gratuities. You can either pre-pay them before the cruise, or have them charged to your onboard account. While you don't have a choice as to how much, you can add or subtract as you feel the need. They will always hassle you if you want to subtract some of the amount, but persistence can pay off if you feel it's warranted.
But I agree with Surfguy - why go into this with a defeatist attitude? Almost always, you'll have a wonderful time. So go into it with that attitude and you won't worry about it.