I would start from my "back to square point". I think landing page should much more information to engage old users as well as new users.
I will give the perspective from user point of view:
I as new user land on any discussion thread to look for the post. When s/he done with thread they look for another interesting thing to see. As there is basically no thread information in sidebars. I click on home page, I see following page. It's basically nothing. Looks like a dummy website.
As a regular user too I some times to to home page and look into that.
Why I am stressing on this: Core of discussion forum is the content not the good looks. If you observe the xBhp, Team-Bhp, India-Mike, Xda-Developers. the design is age old. But one thing is common, on any page you have tons of date to process. On main page of Forum I can quickly see the latest post preview.
If we go to social media design, there we can find infinite scroll to to go next post.
In summary, when a new user lands from a search page, which is case for most of us, user expect to see tons of related stuffs going one level up. This engages the user.
I believe the current surge in searching and landing to CE bases on "Project Queries" happening because, these user don't engage in other discussions. They just create the account to get free project stuffs and don't come back. CE need to hold the these users. These are the use who get nurtured participating in different topics. If I am not wrong many people land here because of "Debate Mastermind", "Gadgets" and "Enginnering threads". Well, I don't know if the Debate Mastermind or Gadgets things brings back the users. But CE is still single place to discuss engineering topic. Specially in-college students.
I think regrouping the topics is required as Ramani sir suggested. I don't see having more number of groups would hurt the forum. I would suggest to add related topics, at end of the thread.
