When my tires are at that point in their lives I think about whether I will be taking any road trips. For local around town driving, I would run the tires longer. If I intended to do a substantial amount of highway driving I would replace them. A few years ago my tires were at that stage and my wife was driving from NY to SC, so we got new tires before she left. A car beside her on the interstate wiped out in rain due to hydroplaning, my wife maintained control. I am more concerned about high speed hydroplaning than a low speed blowout on a run to town.