It really depends upon your goals and what you want. I do take my DSLR and a variety of lenses with me, but that's because I'm an amateur photographer and I tend to shoot most aspect of my everyday life (hiking trips, kids games/sports, events) so my vacation is no different.
I will say this, if you do decide to use something other than a point-and-shoot type of device (phone or otherwise) be sure you are quite familiar with its use, how to shoot the lighting conditions you are hoping for (sunsets/sunrises, fireworks etc.) BEFORE you leave for vacation. Nothing is more frustrating to the spend more time fiddling with the camera than actually taking the shots and enjoying your cruise. And uh... try not to ask other photographers on board for an in-depth lesson on how to use your camera.

Most of us are happy to answer a question or two while we're shooting but we too are on vacation.