With all those things that you have in place, AWS would not be a big win for you, though you still might find some use of AWS services like S3 for reliable object storage, Route53 for DNS, or Lambda for "server-free" event handling. The unique thing about AWS is the huge portfolio of services they have and the absolutely amazing rate at which they manage to pump out new (and useful!) ones.
The Salt is of the shelf, with some bash scripts on top to auto generate some config and make installation of a new server one script call.
We surely could put endless hours into Ops, playing around with stuff etc. but the benefit would be marginal.
Our DNS setup is simple, not much to say, we use DNS Made Easy for failover, we use S3 though I do not consider it "AWS" (S3 is comparativly cheap).
I've wondered about Mesosphere with autoscaling etc. but with adding a new VPS in seconds setting up Mesosphere/Kubernetes taking two weeks would take quite some time to amortize.