I had the same dilemma. In my case, I had the problem on higher speed with the wind getting into my helmet from the chin area. It made my eyes watering all the time. At the end, I decided to go ahead and drill. The improvement was so great that when I sold my '14 DL1000 and got '18 model, the day I brought it from the dealer one of the first things to do was to drill holes for deflectors and install Givi Airflow and new mirrors. Never looked back.
As about drilling, it's my bike so I do the things the way I want... I don't care...
2017 DL1000 White
2014 DL1000 Red (sold)
2012 DL650 White (sold)