Full power should be applied on a go around....every time. If an engine fails in that stage of flight you will need every pony you can muster very quickly. You would be raising the nose to a climb attitude which means a reducing airspeed and getting closer to Vyse. You don't want to reach blue line at anything less than full grunt. Inertia is an important factor when considering a decision altitude for a go around and if applying full flap these should be delayed until that altitude has been reached. Personally my decision altitude has always been 400' in a light/medium twin. If I am convinced all is good for the landing I select full flap and below 400 I am committed. I know some use 300 but the guy would want to be pretty hot on his currency.