Hah, my husband says we do too much. He grumbles. But we do the following:
Fresh flowers in every room
A welcome note with our contact info, handwritten, addressing them by name
A food or adult beverage treat (I ask about allergies and preferences and if they prefer food drink.) The food is mostly something local (cheese, chocolates made down the street, cookies from a local bakery, preserves, honey or eggs from one of the neighbors or a combination of a few things) and I try to cross promote local wineries and breweries for the alcohol
During burn season they get a duraflame for the fireplace and a small bundle of wood for the fire pit
Right now, I am leaving pumpkins and carving tools for guests as a fun treat.
No, it does not improve your ratings. But for me, its all about the experience. We have opened our weekend cottage to strangers, so I try to do exactly what I would do for friends who stayed with us.