get rid of the knobbies unless you're planning on a significant amount of off road riding
+1 When you put slicks on it will feel like you've been riding with a binding brake. According to Sheldon
tread is actually worse than useless on road tires. I've had very good luck with Panasonic RiBiMo tires. My back one did 4500 miles last year with two flats. There are more puncture resistant tires out there (Marathon Plus, Armadillo etc) but I find these heavy and with a harsh ride; the odd, very rare, puncture is a price worth paying for the comfort. It's all really a matter of taste.
And make sure your wheels are up to touring with at least