Those look delicious!
You might try intermingling more umami flavors as opposed to just adding more MSG. The powdered pure MSG can givea metallic taste if overused. This is why I like to use it as an added boost to existing umami as opposed to being the driver. For example, simply adding another umami flavor to the mix can multiply the flavor explosion. You could either mix in or sprinkle on a little Wooster for example. Or you could go for a cheese with a stronger umami flavor, a little bit of a sharp cheddar might be nice, jsut a few sprinkles underneath the American slices perhaps, or sub the American for cheddar entirely if you think you would prefer it that way. Maybe some grilled mushrooms even? You can add a little soy to the mushrooms as they are cooking and you are tripling the umami in that event.
Just food for thought.