Once or twice a year Yamaha runs specials where you buy the motor and they give you the extended warranty. My Yamaha was bought in October and they added three years to the regular three years for a total of six years warranty at no cost to me. Watch their website and wait until they run a deal.
As said above, I would not buy a new motor yet.......but that is your business. I would replace a two stroke at the drop of a hat anytime, but if I had a good running four stroke I would keep running it. I would do the other stuff and keep some money for a new motor in a separate account..... If you buy an extended warranty, with Yamaha I believe you can buy your extended warranty anytime before the first year ends. I am not positive, but I think I am right.