No character that wasn't Squall, Rinoa, or Laguna (and even there, he didn't get that much) got many attention after the first disk.

As for Selphie, I adored her. I found Rinoa to be one-dimensional. Selphie appeared one-dimensional too at first, what's with always being cheerful and optimistic, but as the game progresses, especially toward Trabia Garden's bombing, you get a glimpse of another part of her personality. You see that, despite that hyper, cheerful façade, there is a young woman who hides her own fears and insecurities.