I like to replace tyres before I have to. I feel like it's saved me a lot of headaches over the years. Save a set of old ones as emergency spares, or to throw on to a used set of wheels you acquire, or give to a friend when they need a set. If you decide to run these for a while longer, keep an eye out for sales, you can often find Vittoria Corsa Graphene Pros or Goodyear Eagles for under €30 each.