In general, if you put any kind of lube on the threads, the torque spec should drop a bit because the lube makes it easier to spin the parts. Over-spinning the parts can stretch the threads to the point of damaging them. If you don't compensate for the lube, you could end up over-torqueing things. For example, if wheel lug nuts should be torqued to 100 lb-ft dry, it may drop down to 90 lb-ft with anti-seize. As for spark plugs, I don't know how much it should be reduced, if at all. It also depends on if the torque spec is already tuned for anti-seize. If the official procedure calls for anti-seize, then it's probably ok to assume that the torque spec already compensates for it.