In all honesty, it kind of fits. I mean, that whole evolutionary line were straight Psychic but looked out of place with the other Psychic types. It seems they're trying to give all the later evolutions dual types, and Gardevoir was one that was still one type. Gallade is Psychic/Fighting, but that doesn't fit the more gentle Gardevoir - Fairy kind of does.

Honestly, every time I see them I forget they're Psychic and think Grass. They look so much more like Grass types. >.< (look at Rozerade up there, she could easily be related)

I say wait it out, see how Fairy goes. It might be a fun type. Never know. =)