I have read that glue-on shoes move some horses up. Below is an example from an interview with a farrier:

DUDES: Have you ever seen a good horse turned bad or a bad horse turned good solely because of the shoes he/she is wearing?

VON HEMEL: I can’t give you a specific example but I have heard stories that gluing on Polyflex shoes has helped horses tremendously. Another way I look at it is that people are using them and becoming more popular so they must be doing some good.