I do get that. But I'm wondering if the current design of the forum may to an extent have some connection with so few people posting regularly these days.
I hope not. If we can't get them by the quality of the information we provide, I don't think the style isn't going to make any difference.
I have to disagree. I think everything is part of the complete package that a website or forum offers: the information, the members, the discussions, the look and design. When a forum looks as visually cluttered and un-user-friendly as this one has for the past few years, I can easily picture some people choosing to take their cartoon discussion elsewhere. I know competition from social media sites is hard, but that should be an incentive to make this site as visually attractive and user-friendly as possible.
I did make a few changes. Let me know how it looks for you now. You may have to hit CTRL-F5 to see any changes, but the dropdown menus can be read better now and the quoted posts are more readily apparent.
I pressed CTRL-F5 now and... hey, that DOES look better! It's already a vast improvement from earlier. Well done!
One thing that occurs to me right off the bat... could it be possible to make the "Originally posted by" text parts in quoted comments more visible, i.e. not in such a light grey color? I think the whole layout will 'scan' quicker if they are as instantly readable and big as the text underneath.

Also: This is a bigger thing, but I've been thinking ever since the redesign that the main forum pages look very cluttered, most of all because the headlines are so dang HUGE. The old site layout had a more natural text size for the headlines (i.e. not so overwhelming), and gave a much quicker visual overview of all the topics and categories. Could it be an idea to make all the headlines somewhat smaller?