Pros:
You are on a CRUISE for cryin' out loud!
You get to try those other excursions that sounded pretty good last time, but got voted down.
You can explore totally different areas/attractions/shops in the ports of call.
You know enough about the ports already so you feel more self-confident.
You have a list of "don't need to do THAT agains" from the last one, so you have more positive experiences.
Cons:
The repeat show thing - although we found several "repeat" shows across different ships across several years. I think they rotate these through the fleet (At least Carnival seems to), so you could get a repeat show regardless.
The toilet flushing thing has lost its charm.
The Captain might remember that you were the one who sat in the front row at the Gala Reception and hollered "PIRATES!!!" when he was introducing the Security Officer.
The Piano Bar guy still only knows the same 7,284 songs.
There will be confusion when you tell the bartender "the usual", and he asks "from which cruise?"
You will STILL pack twice as much as you need, although you told yourself you had learned your lesson last time.
... did I miss anything?