Kach, Sounds like you take care of your mower like 99% of the people that own them. (Hope you're using synthetic oil
)
IMO, the last component to go on that level mower is not the engine. Usually the wheels, bagging system or another part break. Many times not worth the fix.
With the cost of blades I'd just replace with new.
Also, the single most important replaceable tune-up item is the air filter. It takes the most abuse.