I voted yes (shoot me, right?).
I am not going to say I am an all for Illia, she isn't one of the greatest characters ever, she didn't add much to the game. But we have to realize that her character was never supposed to do much in regards to the story. The most she actually does is give you the horse whistle and help you restore the dominion rod. But, her intro didn't really set her up for much. She was Link's best friend, a character type we have seen before. Her addition to the story, IMO, is to give the player motivation.
I would like to use Aryll from WW as a similar comparison. She does very little except give Link his telescope at the beginning. Other than that, Aryll gets kidnapped. Sound familiar? The only difference is that Aryll isn't seen as a useless character. Illia does the exact same. She gets kidnapped as motivation to get the player thrown into the events of the game. Without this kidnapped character, there would be no need for Link to ever leave his small home and get involved into anything. We are reminded of this in TP when Midna uses Illia and Colin to goad Link into listening to her (rooftops of Hyrule Castle).
Illia had much more potential, I do agree, but I don't believe she was set up for much more. She is just too often compared to Saria (not sure if correct spelling) instead of other motivation characters.