I think that a useful feature in this forum could be the ability to intentionally respond to threads without sending them to the front page and without notifying respondents.
Such feature already exists in image boards like 2chan already implement this feature since long ago. It can add incentive to discuss older threads without the fear of 'necro bumping' and also when users want to respond to a thread critically without promoting it via bumps.
Now I think it'd be nice to allow for users to choose if they'll bump a thread.
I have to disagree with the underlying idea. I think it's up to each individual to decide if their post has enough substance to warrant bumping an old thread to the forefront by rehashing a discussion. Sometimes things have changed good or bad that definitely warrant a necrobump to bring this relevant information back to life.
The point Upgrade00 fits this as well. If the information is worthy of necrobumping then it should be worthy of restarting the discussion for anyone who notices it. You can also post a heading that you have necrobumped the thread and explain why, if the purpose is more of a PSA or FYI style post.
The other option is to create a new topic that centers around whatever you wanted to add to that discussion, and link to the old thread. The problem here is if the older users are still active they don't get a notification in "show new replies to your posts".