the stories would have benefited from our heroes never knowing which face would go with a tummy that held a Trill.
I don't understand how you think this would work unless the host changed every few episodes. Could you give an example of the sor of story you mean? A description in a few sentences?
The concept of a "host species" was the unnecessary one, and rather uninteresting in the end.
Unnecessary? I can't think of another way to pass on several lifetimes of experiences from one body to another without invoking some kind of magic.