What are the benefits of using WCF?

WCF is not a replacement for SOAP, and indeed, SOAP can be used as the serialization format between endpoints for communication. SOAP the standard also doesn't really define what goes in the message body, so in the case of WCF-to-WCF communication, a SOAP envelope is used, but the content is binary, so there's your primary advantage, at least in terms of performance. Another advantage is that the programming model of WCF is, or at least is intended to be, much more straightforward; especially since it sounds like you're really just using Web Services to communicate internally. In this case, most of the work would be up front, configuring endpoints (though consuming asmx WSDLs is obviously very easy in .NET).

I'm no expert in WCF, but what I do know has been from .NET user group presentations by Juval Lowy (who wrote the O'Reilly WCF book), his site has a decent amount of information in the way of screencasts and samples in the Resources section, in addition to the Microsoft sites (have you checked Channel9?).