Thanks, guys. Great responses.
My car looks too high in the back. That's my main reason for lowering. Maybe it will improve handling, but I'm at-the-limit so infrequently I doubt I'd notice.
I think I'll leave the front as is. It looks fine, and I'm running 11" wheel widths in front so don't have a lot of clearance.
I'm buying a new (to me) race car soon, so I'll only be taking the ZR-1 to the track occasionally. Otherwise the coil overs would be worth considering.
Gunny, next month (March 13) I'll be at Atlanta Motorsports Park in Dawsonville, GA (home of Awesome Bill Elliot :-). It is a really fun track. Check it out:
http://atlantamotorsportspark.com/about/circuits