As somebody who runs a discussion board for local people talking about issues and history, I have to run a much more socially-oriented board than this one, so I do have to have certain user interface aspects (user avatars) and social media connective tissue that a technical board like this doesn't necessarily need to have.
That said, I can immediately see some changes that would be beneficial...
1) Make the site menu more prominent. I've been here several times before, but it took me a few minutes of looking around before I noticed the "login" link. At the very least, the fonts used are way too small, and no, I'm not in the habit of resizing fonts on websites -- in fact, I rarely do that.
2) Use smart login redirection. After logging in, it should take you back to the page you logged in from. In the fork of phpBB2 I used for my site, I applied the "Login Redirection" mod, and its effect has been pretty powerful. For bonus points, place the login form at the top of every page as long as the user isn't logged in. It's just convenient.
3) Move the "Post New Topic" and "Post Reply" buttons to the lefthand side. They're currently on the righthand side, and it's not where my eyes expect them to be. In fact, this may be the only board I go to where buttons like this appears where they are. In user interface development, it's always important to understand where the eyes want to go. For bonus points, make the buttons stand out more.
4) Provide some way for users to share topics with their social media friends. On my board, it hasn't brought in an avalanche of traffic, but it does help build awareness of the board and can sometimes add more attention to a topic that wouldn't get it otherwise. I have found that some topics that should generate excitement won't until somebody outside the board is told about it.
5) It would be nice to be able to jump to another forum from any page.
6) It would be nice to be able to do a quick search from any page, with the ability to set the context of the search, such as being able to search within one long topic that I'm current viewing.
7) In general, pay more attention to making site navigation more obvious and links/text/colors more noticeable and crisp.
8) Make the site feel less boxy, but I realize this is a purely technical forum, so just see if you can "sand off the edges" a bit.
9) Rename "sticky mail" to "private mail". Clear, common nomenclature is important.
Beyond these ideas, I would recommend making changes incrementally, and given this board's longevity and committed user base, seek agreement on ideas using snapshots and polls before implementing. There's nothing that says you have to do a full makeover in one shot. It's easier for users to adjust to incremental changes. Most big sites that users are accustomed to change incrementally anyway.
Hope these ideas help!