Hey Trueblue, density altitude is possibly the single most important factor in exterior ballistics predictions. However unfortunately outside of aviation circles it is not widely known or understood, nor is it used by software, making it essentially pointless.
DA gives us the effective resistance of the air on the bullet given the temperature, atmospheric pressure, altitude and humidity. Most programs must combine these factors if you enter them in, and make something similar to a DA calculation, but as a stand alone factor it could be viable replacement for the weather based variables we input.
By all means, use a Kestrel
4000 and log DA when shooting and you will be able to determine how your load performs in different places at different times of year, at different altitudes and temperatures with more accurately than by temperature and altitude alone.