... when an illegal sneaks into Texas, does the collective IQ of the state go up?   How much?  Is this a general benefit to the country as a whole?  Is Texas an economic threat to the rest of the country as the people in the state get smarter and less shiftless from the illegal immigration?  

No, perhaps the aggregate IQ goes up, but I'm betting that the averge and median IQs either remain constant or take a slight dip, particularly if the illegal immigrants' age distributions skew toward the younger age groupings.

oh lordie... did you really miss that one?

It depends on where you are. If you are in Texas when he sneaks in, then the average IQ goes up, if you are not in Texas, then it goes down.