I have a three flat rule, 3rd flat, time for a new one since the road contact area is probably getting thin. Most road tires have a rounded profile when new. When you start seeing a 1/2 inch or so wide flat area, time for a new one. I have tubes with 4 of 5 patches, but I rotate them from bike to bike as I repair them. I've also glued patches inside the tire casing to keep a cut from getting worse, or letting other foreign matter inside to damage the tube; usually works for small cuts.