I think that the tunnels on alot of rides don't do too much for the 'scare factor'. I personally don't like the coasters that drop into tunnels (i.e., Desperado) because if a gust of wind catches you the right way, you can get a really horrible whipping effect on your neck. (Your head bends back too far, too fast) Don't get me wrong, I still love these rides, but I just don't like the tunnel after the drop.
Anyway, more on topic, I agree that tunnels with fog, lights, etc. have more of an effect on the ride. Going through a tunnel after a drop that is completely dark, though, is kind of pointless, I think.
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If bees make honey, then do earwigs make chutney?