Changing the tires will have a much bigger effect. But its still going to be a touring bike with touring bike handling. I don't think it will change it much.

I have a LHT that I orginally had 35mm tires on it. I change it to 28mm tires and I actually hated it and I felt it was slower. Plus I liked the cush of the 35mm tires.

Its funny, next year I'm planning on doing some centuries on the Trucker as apposed to my Madone. I want something that is going to be more comfortable with higher bars.