I think Rikku and Auron could be the classic romantic couple: older mysterious if rather gruff man attracts lively, optimistic younger woman. I don't know about everybody putting them together though. Eg in fan fiction sites, Rikku/Auron pairings seem rare, and you get lots of comments about it being pervy.

I didn't notice about the armour in X2, that's really interesting! Of course they don't immediately hit it off. When Rikku says, "You don't get me at all, do you?" (in the Thunder Plains Agency) she's talking mostly to Auron, after his comment, "She's worse than the storm!" But that happens a lot in romantic novels.