1. It's nice to see you're already communicating with the users. It's something I could never get previous leadership to do. Keep it up! You won't be able to bring them everything on their wishlist -- but don't let that stop you from telling them what you are bringing them, and why the other stuff got pushed lower on the priority list. They're reasonable folks; as long as you're working with them, they'll be on your side.
2. Small changes are better than big ones. Don't push ahead with a massive, grand plan and assume the community will jump on board (like video and beta). If they tell you they don't want it, they don't actually want it. When in doubt, trust Tim L. and Tim V. Nobody cares about the site and its users as much as those two.
3. Build for the community you have, not for the one you want. Don't chase the hockey stick. It's not going to happen. But there's still a path for evolving Slashdot to support an incredibly broad tech/geek community.
4. Nobody should make decisions about the site without being an active user.
5. Ask the community for help more often. The biggest area that needs it right now is submissions. They're the base from which all content flows, and they've been slowly drying up. Submission needs to feel less like screaming into the abyss. Consider reviving the IRC channel to give people direct, instant access to editorial. Try to find ways to solicit particular submissions from known experts. (For example, a submission about a new C++ release from an actual C++ engineer is worth its weight in gold.
6. Reward readers for doing things that benefit the site. Used a mod point? +1 subscriber (ad-free) page. Got a score:5 comment? +10 pages. Accepted submission? +10 pages. Or more. Be generous; these are your most valuable users.
7. Empower and invest in editorial. It is literally their job to know and understand the community, so they shouldn't lose fights centering on the community.
8. Ads have been in a bad place for a couple of years. Pulling it back will cost you revenue in the short term, but may ensure the site's sustainability in the long term.
9. Slashdot's founder, Rob Malda, still cares deeply about Slashdot. I'm sure he'd be willing to offer some advice.
You've been saying a lot of the right things about Slashdot an SourceForge. I sincerely hope you make it all happen.
Best of luck,