If I look at the forums from a reader-specific perspective, it looks really creator-exclusive. If I'm not a creator, there's not much that I can relate to on the forums. If I wanted to make a thread about this new show that I watched, I would feel a bit silly posting it on a forum where everyone is serious about seeking help and improvement about comics. It might feel too serious for the average reader to want to contribute. And perhaps also too "comic-specific".
Looking at it from a different angle- if I'm only a reader, what would I have to contribute to the forums that isn't about making comics? I could only contribute my interest and opinion in things. My knowledge and experience would be limited compared to people who have drawn and written for a lifetime, so I'll talk about things that are easy or familiar or "acceptable" for me to talk about. I think the forums don't really encourage those sort of topics.
I don't know if this would be considered "useful for readers", but you could have an "Off-Topic" or "Anything goes" category that specifically affirms talking about things not necessarily comic related. Even multiple off-topic categories would be good. I know there is already an "Uncategorized" category, but the description of it seems too serious to encourage really non-comic related things. I think a part of the reason why the forums seems to cater mostly to creators is because the categories seem to cater mostly to creators. Naturally, the threads created within them also cater mostly to creators. Also, I noticed that most of the categories don't have descriptions on them. They may seem self-explanatory, but it would be better to have clear descriptions of what is encouraged and what isn't. Even better, if those descriptions invite me to post about things I can relate to I would feel much more comfortable to contribute.
You could also do a front page Spotlight feature about it to invite everyone to join in.
I think you've got the helpful/useful part covered- if a reader was experiencing some problem on the website, it'd be easy to use the forums to ask for assistance. There are clear places for them to do so.
I hope this helped somewhat.