I'd probably get a set of Finspeeds if I were going to track them a lot. I really like their designs as well.

 

Champion Motorsports makes some pretty light wheels. I think my RS98 rears are 19lbs. But I could me mistaken.

 

Less rotating mass has always made a huge difference on the race track in both accelerating and braking, overall handling and steering response is greatly improved as well. At a huge expense I was using true ultra light magnesium wheels on my roadrace motorcycles years ago. I switched from OE hollowspokes to Victor Innsbrucks in 18 a couple of years ago. Not an expensive or high end wheel but look good, very light and good quality. The first drive in the canyon, I could definitely notice a difference in handling.