With the cost of ammo (not to mention the availability), I try to keep my skills sharp with my Airsoft. While the weight and feel (not to mention recoil) are obviously different, I believe that it provides a lot of benefits (especially compared to doing nothing at all).
The most important skill Airsoft works for me is point shooting. I place a sticky target about 15 feet away and start from the low ready position. I bring the gun up without using the sights and try to get as clost to bulls eye as possible. When I practiced all the time, I was grouping about 2 inches consistently from 15 feet away. You should obviously get an Airsoft that is a good replica of your carry gun (possible even fits your holster). Practice drawing from concealment and shooting as quickly as possible after drawing. In a real life defensive situation, pretty little groups is highly over rated. Getting lead on your target first is what often wins the fight. I observed a bunch of thug looking characters at the range holding the gun sideways and just pulling the trigger as quickly as possible. While their target looked more like a shotgun blast, they were still hitting the target fairly regularly. My point is that a lucky shot (or unlucky shot if you are the one getting hit) still counts. I'd give up my ability to make pretty little groups in exchange for draw and shoot skills of the legendary gun slingers.
Of course you need to stay on top of your training and not get sloppy or develop bad habits. My years of punching pretty little groups actually helped me out when I tried IPSC for the first time a few years ago. There is a lot to be said for muscle memory, especially trigger control, and point shooting. Good luck!
The ATF should be a convenience store instead of a government agency!