I added insulation to my attic rafters, but should I have left room for airflow?
You can buy air ducts that staple to the inside of your roof above the eave vents and fit between the rafters.  The will hold open an air gap of approximately 1 inch to allow airflow past a layer of insulation.  The ones I've used are made of styrofoam and IIRC they cost around $2.  You should be able to find them near the insulation in your home improvement store.

EDIT: They are called baffles or rafter vents; this is how they're installed: