A few months ago I bought a Sig Trailside and I take it to the range with me every time I shoot. I put about 50-100 rounds downrange with it and my pistol shooting has improved dramatically. The recoil, grip, tirgger, and sights are totally different than my M&Ps but it has still improved my overall shooting. I would think and airsoft weapon wouldn't be much different especially if you can get one that shares some similarities with you primary weapon. Any time spent shooting properly will improve your shooting.
What I don't believe in is simply firing rounds down range. When I taught TKD I always stressed GOOD practice. If you practice your technique properly until you get tired and do it 50 more times improperly, you are teaching yourself to do it poorly more than well. If you practice a bad habit when you are shooting you are training in bad habits. If you practice good technique and habits you will grow more in your training.
I guess what I'm saying is if the airsoft gun helps you practice good technique and habits then it will be beneficial. If it encourages bad technique you are better off not using it. Whether or not it is exactly like shooting a real weapon isn't nearly as important.
Why has INTEGRITY become such a rare commodity?