We just went on our first cruise ( 4 night Wonder) and we loved going to a different restaurant each night and enjoying the atmosphere and the menu and our attentive waiters. Not to mention that the meals were already paid for!
But, if you decide for some reason not to go where you've been assigned, you can always order room service or go to Palo's or eat from the stands at the pools (but I think they close around the dinner hours).
If you don't show up, your wait-staff still have other guests to attend to. I also would think that you shouldn't deduct the tip.
We couldn't resist trying most of the food during the day (buffet and pool stands), but by day 3, my kids finally realized they needed to save room for dinner. The last two nights they finally had room to have dessert!
I just think that since this is your first cruise, you will probably not feel like staying in your room rather than going out to dine.
We didn't eat at Palo's, but I definitely think this would be a great alternative, especially for the last evening since your restaurant will be the same as the first night.
Just my thoughts.