Gee, a wisecrack just because I pointed out that 0.1 g/cm3 might affect the result very little and you point out you fudged the formula to take into account if the water is cold or warm. That means that with the formula, when the lure is built, you can be confident that it might float, be neutral, or sink when it's made depending on the time of year you fish it.
There are variables that affect the lure, sure. The 0.1 is one of them. But not much more than other things like the temperature or a fudge factor in a calculation.