Thanks for the reply Bill. That makes sense about the butter making the waffles more tender. Also I had the same thought about buttermilk shortly after posing the question; that it would take away from the sourdough flavour (especially with a more mild starter).
As for cheese on waffles, growing up my family did regular Sunday brunches, usually waffles or pancakes, and a cheese plate was always on the table. I love the combination of a really sharp aged cheddar with maple syrup drizzled on top. Everyone I've introduced the combo to loves it. Add to that a slice of savoury sausage and you've got one very delicious and complex mouthful!
Marscapone or a fresh chèvre with fesh fruit salad is another awesome topping combo.