when the temps start dropping, do you run the HS a bit richer or leaner...???

richen it up

+1 and hotter plug.....

Yep, cold weather is normally accompanied by low humidty. So there is not as much moisture in the air. Fatten her up!

Run richer and you can add aluminum foil around few fins to make sure it goes up in temp.

You can also read this http://www.myrcbox.com/?p=3899 this explains engine tuning according to weather.

When running in cold weather i take an old sock and wrap the fins of the cooling head, use a hot plug, richen the motor.