It's one of reasons why I have switched from wxSmith to wxFormBuilder. I haven't found how can I create more than one "top level" resource in my XRC file using wxSmith. Once I created a top level window, everything needed to be a child of this window. Create a set of popup menus? Forget it. Create a set of dialogs along with your main window? Forget it. wxFormBuilder allows more than one top level resource. Moreover, wxFormBuilder can create only a XRC file - well, it creates a code, too, and you can paste parts of the code in your own code.
I am curious what I have missed. I am a "XRC user", too.