Last year I changed both tyres because front one had developed a blister!
These tyres were'nt even really worn,no flat to speak of,profile seemed quite good,BUT what a difference with a new set,handled like a new bike!You don't realise how much your tyres change because it is a gradual process,but new ones give an immediate difference!WOW!
Like the other post said,don't forget to scrub them in,especially if you ride in the wet.
Stevie