Well…the definition of a ‘lurker’ is someone who lurks, so it’s unsurprising that none of them have every spoken up. 
(not sure if you were going for tongue in cheek there or not)
That said, I’ve seen some regular 'dopers modify their stance on this subject over the years. I don’t have any specific examples (too lazy to search and don’t remember who specifically atm), but I’ve noticed the change in attitude from uninformed and leaning towards at least some of the Truther/CT claims to opposed, and I think it was entirely based on these threads going many pages, and a lot of 'dopers jumping in to make the Truther crowd look like idiots. YMMV, but that’s my take.
But a lot of folks don’t care enough to get involved, so only have a vague idea of the topic. Those folks aren’t likely to slog through the entire 400+ posts, but maybe are just skimming. And it might be a few posts that catch their attention, gain their interest or otherwise get them thinking. The fact that the Truthers don’t really have a basis for their bullshit, coupled with the overwhelming evidence of the ‘official story’, and further coupled by the fact that most of the people in these threads are adamantly opposed (and vocal about it) to the Truther non-sense might make a difference.
Regardless, I think it’s important to make these folks look bad, even if it don’t convince anyone on the fence.
No…there is no point talking to him or her, since they aren’t listening. It’s like the religious thing, or Evolution…you are never going to convince the faithful. Never. The thing is, it’s pretty obvious to even the casual viewer that good ole Mozart1220 is not engaging in the debate, is not providing any evidence, and basically doesn’t know what he or she is talking about. Amadeus is obviously ignorant of even the basics of the debate, and is simply parroting the same things over and over again. And each time he or she does that they come in for another round of beating. I’d say that the thread will bump along as long as Mozart et al keeps coming back to take more lumps, or until a friendly Mod puts us all out of our misery for this round of 9/11 Whack-A-Mole.
I wish you luck, but I think you are bound for disappointment if you think you can make such folks as these engage. Personally, I don’t think it’s working out really well for them at all…the Truthers are, as usually, taking the same old beating.
To paraphrase, the crazies kept coming the same old way, and we keep beating them the same old way. To mix paraphrases, I think we need to keep up the skeer…
-XT