If you are trying to communicate with a vendor that uses SOAP 1.2, it almost always seems to come down to guesswork. What set of properties do I need to specify before they accept my request? The WSDL gives you an object schema but it's not sufficient for the masses of WS-* extensions that you might have to support. Meanwhile, the vendor just exposes the WSDL and assumes that's sufficient "documentation" for clients and you don't need any examples or explanations or other info. I find the best way to approach this is to open Soap UI and start messing with settings until requests are accepted. There's no point asking the vendor for documentation because they probably don't know themselves.
Also, speaking from the perspective of a framework developer, I mainly start to pay attention when things stop working or clients are having problems. SOAP 1.2 doesn't have any more problems, but the problems are proportionally harder to solve. No matter how good your tooling is, it's not perfect, and it's a lot easier to look "under the covers" for RESTful services than for SOAP services. Of course that could also be attributed to the hellish nature of WCF, and not SOAP 1.2 per se.