If you're going to Palo, then you may want to tip more because the service will most likely be outstanding. Same goes for room service. It's customary to tip a few bucks for room service.
I don't tip at breakfast and lunch because I do tip in full at dinner - regardless of whether I ate there every night or not. However, if I skipped dinner my entire cruise, I'd probably leave a few bucks whenever I sat down for lunch or dinner.
If you don't intend to use your table, you should inform
DCL or - at the latest - your head waiter when you board. There's probably a family wanting to sit together, someone wishing to change rotation, someone wishing to sit alone, someone wishing to change dining times, etc so please give them a shot. If you prefer to hold the table "in reserve" just in case you might use it, then I definitely think you ought to tip because you've denied the wait staff a chance to earn that tip otherwise.
JMHO.
Sam