These were a treat when we went to my Aunt's home at Christmas as kids.
She added chopped maraschinos to the mix. Sometimes even coconut too.
Gave a nice colour lift from an otherwise drab brown!
As per JuliaSB, brown sugar was used.
Butter is the secret ingredient ... AAshley333, might I suggest that if you are changing anything, just go with more graham crackers and a thinner spread/topping? Though TBH, I think for most enjoyment you would be better to stick to the recipe in this case.