45mpg is good. I get a little more than that after intake/muff/carb mods.
As for the spacer mod, I had the DJ kit before I knew how to do it. So personally, I can't tell you yay or nay, but after reading about it, you may want to be a little familiar with the parts of a carb first.
Oh, and watch out... this bike gets addictive!! You may not be able to leave the garage after you pull your first piece apart!