Aluminum frames have been around for a long while. Years ago I had a Colt Commander which had the aluminum frame. I shot the snot out of it for three years or so with no visible wear.
The Kimber aluminum frame will wear as well a steel frame gun INHO. I have a friend that has a Tacticle Pro, (4" barrel?). He has put thousands of rounds through it and it is still tight, extremely accurate and reliable.
As far as hearing that you should stay away from aluminum frames, it is not true.
D