First off, congratulations on passing! That's awesome.
I believe both exams compliment each other well, the ACMP and CWNA that is. As you said, the CWNA is not vendor specific so you'll find it focused on more of the industry standards that are great fundamentals. I personally don't feel it would be a waste of your time by any stretch. It was worth it to me. As for the AWMP - I enjoyed it but I recommend some hands on time with the product before testing.
Cheers and congrats again!