As I recall, iPhones have 8 megapixel cameras with pretty good quality, don't they? All of the shots I've had accepted to iStock were shot with my 8mp Olympus C8080. In fact, my second most popular photo on iStock is the one I used for this icon. The lighting in your photo of the lamp post is pretty much perfect, as is the composition, and unless it's noisy at 100%, I'd bet you your next ticket to Portland CC against a coffee drink the next time we meet at a fan event that this lamp post photo would be accepted.

As for the competition thing, I can definitely see why you wouldn't want to do that. That said, I doubt your brother would mind it if you submitted your fun shots that would qualify and this one definitely would. And the idea that someone is willing to pay you for your photography is a real boost to the self esteem, believe me!