don't the LW surveys consistently show that there isn't a large IQ increase in less wrong readers?

Maybe I'm misunderstanding, but if you mean "... that there isn't a large difference between the IQs of LW readers and those of the general population" then no, the surveys appear to show the exact opposite: so far as one can tell from these surveys, the LW population appears to be something like 3 standard deviations above average.

For the avoidance of doubt, this is perfectly consistent with its being a really bad idea to be dismissive about people with average IQs -- though as it happens I don't think Alicorn actually was, and in particular she didn't refer to anyone as "IQ 100s".