I've seen some really good cosplays of him. I don't know how anyone sees. I think they're a little transparent if you have your eyes right up to it but idk.Lots of cosplay outfits make it hard to see. It's about whether or not its worth it.
Never figured I'd see a Homestuck fan on RT, but in answer to your question yes I will be cosplaying as Doc Scratch at SDCC. Here's a quick pic to give you, and other curious folks, an idea of what I'll look like.