At my old house I had my furnace cleaned yearly but never touched my AC. The company that installed it never even suggested it, though they sent me a post card yearly about the furnace. In 20 years I needed furnace service once, but never AC.
At my "new" house (7 years old) they cleaned both last year as a condition of my buying the house (it had no maintenance since installation and that seemed wrong). Now the company (a different one from the old house) suggests cleaning both again. I don't mind doing the furnace, but I wonder about the AC. Any strong opinions on the cost effectiveness of spending $100 for yearly maintenance on AC?