I have been using the same taps for 15 years and have not even resharped any. They all still work just fine as they are made to tap steel and all they ever cut is wood and brass.
I agree 100%. If you have been tapping 3/8x10 for only a a couple years and ONLY into wood, and it seems dull, one thing to try is to soak the hole with super glue or a fast dry sealer, then try tapping it once it's dry. If the wood is too soft, I.E. soft maple, it will appear to be a worn out tap, but in reality it's the fact of, it's too soft of a wood. I have 3 3/8 taps and have had 2 for the last 7 years or more. I have tapped all kinds of wood and delrin, and even steel and brass, and they are still as sharp as when I bought them.
Dave