Let me break it down.
cheese on toast > cheese sandwich.
And while
cheese on toast > grilled cheese sandwich
it can not follow that
grilled cheese sandwich < cheese sandwich
due to what if often referred to as Cheddar's Theorem (Almqvist, Poole et al - 1974), which clearly states
D = -k(dT-T0)^2 + F
Where D is some objective measure of deliciousness, dT is the temperature of the cheese above room temperature. T0, k and F are all positive constants, with F dependant on the type of cheese, T0 on the eater's pain threshold, and k on the delivery method of the cheese.
This produces a graph much like the following:
As you can see, cheese is quite delicious at room temperature, and even when refrigerated to some extent. But beneath some key temperature it becomes too cold. As you heat cheese above room temperature it becomes yet more delicious, and increases inversely proportional to the square of the temperature difference approaching some ideal temperature. Beyond this the cheese is too hot, causing discomfort to the eater.
To simplify: within typical culinary temperatures, cheese gets tastier the warmer it is. Thus a grilled cheese sandwich is always going to be tastier than a plain cheese sandwich, even before you take into account the different k-values of grilled and raw bread.
