When there are "no actions attached" the spec says this: The action "cancel" is always allowed. If there is no element, the user-agent can use a single-stage dialog or view. The action "execute" is equivalent to the action "complete".
Multiple payloads in an ad-hoc command: When the precedence of these payload elements becomes important (such as when both "jabber:x:data" and "jabber:x:oob" elements are present), the order of the elements SHOULD be used. Those elements that come earlier in the child list take precedence over those later in the child list. -- if there are two forms and an OOB you pick one, you don't render them all
I read that as meaning that you show those first and use their values first (if multiple conflicting values exist) but that you should still show all of them. I also just re-read that section and have literally no idea what it's talking about anymore. I think what you're saying would make the most sense, but I'm not sure that's what the XEP actually means.
