First of all, there are only 3 important characters in this book. They probably either represent the id, the ego, and the superego (obviously Lord Henry being the id, Dorian Gray being the ego, and Basil being the superego) or represent Dorian as a normal person with Lord Henry as the devil and Basil the voice of reason. I can't believe you're not even going to discuss this possibility at all!
Second of all, one of the major themes of the novel is paradoxes. Obviously. I mean, that's what Lord Henry does, starting with his very first speech to Dorian Gray, in which he uses a speech about how terrible influence is to influence Dorian Gray. He's even called the "Lord of Paradoxes" at some point, I believe. Even in your own interpretations, you point out the fact that while Wilde's philosophy is that aestheticism is its own reward, he uses the novel to prove a point rather than letting it stand alone as an artistic piece, and that Wilde seems to be against influence except for when Basil is trying to influence Dorian Gray. Paradox is an important point to recognize in the novel. Perhaps it reflects Wilde's frustration with the hypocrisy of the upper class. Perhaps it reflects a philosophy that one can never really be sure which philosophy is right. I don't know, but at least mention it for heaven's sake.
Additionally, the fourth character in the book, Sibyl Vane, is certainly worth a mention in the character section. You're not going to point out the fact that she represents Dorian Gray's ideal of beauty, which of course can never be realized because it doesn't really exist? The scene where Dorian and Sibyl talk after Sibyl acts badly for the first time, Sibyl suddenly knows Dorian's name for the first time in the whole novel. In fact, the book even points that out to you specifically. "'Dorian,' she answered, lingering over his name..." (pg. 62 in my edition). That's because in that scene, each is seeing the other's true self for the first time, right? This is a turning point in Dorian Gray's downfall.
Furthermore, the name Dorian Gray must mean something. I mean, the narrative rarely refers to him as "Dorian." It's always the full name, "Dorian Gray." Same with Sibyl Vane. Why? This is the kind of stuff I want you to tell me, Sparknotes!
...I think I'm getting too old for this website. Unless there's something I'm missing, does anyone know of a better one? Or can you guys edit or something?
P.S. Realizing that I have no life while typing long, angry comments on Sparknotes....*sigh*.