Commander Contrarian: Justified. Decker does know the refit Enterprise better than Kirk. Countermanding an order from Kirk actually saves the ship from face-planting in an asteroid. Less justified later, as he makes some suggestions that can at best be excused as understandably irrational from a guy who just lost his girlfriend.
Ilia (Persis Khambatta)
The Artifact: Ilia was also intended to be a new character on Phase II, and screen tests of Persis Khambatta in a '60's-era miniskirt uniform are extant.
Deadpan Snarker: At least according to the background information that Gene Roddenberry wrote for the character's species. He described the race as having an extremely developed sense of humor with a delivery so dry that they seem very cold and aloof to outsiders. Most other races don't ever realize when a Deltan is making fun of them, which probably explains the Breathless Non Sequitur she delvers to Kirk:
Ilia: My oath of celibacy is on record, Captain.
Informed Attractiveness: We're not saying that Persis Khambatta isn't attractive, but Ilia is one of a select group of Trek characters with less hair than Picard, and yet several male crew members get all goofy around her. The novelization explains this as her race releasing pheromones whenever they're around unfamiliar males - so it's not really because of her attractiveness sometimes; they just can't help their reactions.