What would you pay extra for?
Soda. (that's the ONE difference between Royal and Disney in terms of being charged on one and not the other, for things both lines have)
Alcohol, bottled waters (normal water and sparkling), fresh squeezed OJ in the mornings, espresso drinks, fancy Tazo tea, fancy hot chocolate at the espresso bar, Ben&Jerry's ice cream...specialty dining venues. Gambling.
This is a Vision class ship, and we basically liked our cruise on Vision. The only con, to me, is that they still allow smoking in the casino, and Vision class has a centrum that the casino leads out into, so the smoke can end up in the Centrum airspace. This became an issue for me because we were in a new Panoramic Oceanview cabin just off the Centrum on deck 7, and we had bad weather for around 2 days so ALL the smokers were using the casino instead of the outdoors spaces. By the end of day two the smoke wasn't just going up, but it was going down to deck 4 as well.
On the other hand, the Schooner Bar isn't near the casino, and it was a very funky cool place to hang out without smoke problems.
It's a pretty ship, it's small so you won't get lost.
You will likely wish you were on a longer cruise. Save money so you can book onboard.