Charles 1) You should have in your set up notes the distance from the bottom of the air dam to the ground (if not, bad boy, you need to know this and have other measurements recorded,too).
2) If this # was less than the sidewall height of your tire at set up pressure, it means that you have front lift (as jl222 said "eyeball engineering"). At the speeds you're running front tire growth is not going to have a big effect on the tire height.
3) I think you'll learn more in the tunnel (for the equivalent $$ spent on data acquisition, at least chassis-wise) than buying a data system for next year, unless you've got the $$ to spend on both. I'd gladly discuss this with you (we need to do lunch during the upcoming holiday season, anyway.)
4) I'd gladly help you with a plan of attack for the tunnel which will optimize your efforts (I do have some experience here), and accompany you to assist.
vic