Your cat may be spraying because he is starting to have urinary tract problems. My cat started doing this also, after years of very consistent litter box behavior. So I took him to the vet, and gave him some medication for a week or so (forgot what exactly, probably antibiotics), and put him on the Science Diet for cats with urinary problems recommended by the vet. He did get somewhat better, but he gained a lot of weight and became very lethargic. He stopped playing. His litter box habits were still somewhat inconsistent.
I then ran across a book called Dr. Pitcairn's Complete Guide to Natural Dog and Cat Health (the title may not be exact). There are recipes in the book for home-made pet foods. I began switching him over to this diet. Over the next six months, he became lean and active again and all the urinary difficulties went away. He started playing again and is still going strong. This all happened several years ago. Since then, every time I have tried switching him back to any commercial food, no matter how high the quality, the urinary problems return within days. It only takes about 30 minutes to make a week's worth of food. It costs me about $15 a month for this diet. The recipe I like has cooked polenta and raw ground turkey. To this I add crushed garlic, a little flaxseed meal, 2 eggs, and a quarter cup of oil. Sometimes I steam some frozen mixed veggies, mash them and mix it in.
My cat had been eating high-quality pet foods like Iams, Science Diet, Nature's Recipe, etc. I have since found out that even these pet foods don't offer the nutritional balance that some sensitive cats need.
I think the reason that he started spraying was that he had associated painful urination with his litter box, and was trying to find a place to pee where it wouldn't hurt.
Another excellent book about pet health is The Nature of Animal Healing by Dr. Martin Goldstein.
I wish you all the best in health.