Did you know that while Sora was the main character, Riku was the real driver in the story in most of the major games, either through people searching for him or from him helping to drive events through the background? If you ask me Tetsuya Nomura is extremely talented with weaving his characters into a believable story-line. And most importantly I think it would be a good idea to test the sustainability of green energy balls, like those found in the game. Imagine the practical uses of those devices in situations where you didn't have time to sustain yourself through food!
I agree that Riku is more of a main character than Sora, and that Riku's the one who pushes the story line. I think they should make a Kingdom Hearts game from Riku's point of view, even if we know part of his story line from the Kingdom Hearts games.