What I do is quickly scan down the list of threads, if I started it, and folks have posted replies, I feel obligated to continue on and reply, since I started it in the first place.
Second order of priority, interest. If I am really busy, "new pictures of fluffy" gets passed over until I have some more time.
I always try to say a quick "hello" to new members. And no one expects you to reply to everything
One thing that I have noticed, new threads starting that could have easily been added to a pre-existing thread. I see that all the time, parallel discussions on the same topic.
Keeping on topic would reduce the clutter as well, I have seen entire threads start out as important discussions only to turn into dribble about completely unrelated subjects.