I have had my negative experiences turned into positive ones after I completed the surveys.
Without naming the hotel here, my wife and I were staying at this westin in one of the cities downtown for new years eve. I requested a microwave. The hotel charged me $35 per night for a microwave. Never in my last 5 years of staying in hotels have I encountered this.
I simply paid for it and left after my vacation was over. However, in the post stay survey, I mentioned this point and noted that such thing never happened in any of the SPG properties that I stayed at.
A week later, the property manager contacted me via email telling me that the microwave charges are being reimbursed to my cc. And the amount was in my account 3 days later.
Sometimes it does help to fill it out but try to be considerate in the language you use.