I think the first step in improving the quality of hooves is good nutrition/well balanced diet, and a regular schedule of trimming and resetting the shoes.
As for hoof polishes and conditioners, I would stay away from the polishes. I have never used them, but I think that they are mainly cosmetic, and are probably drying to the hooves. I do think that hoof conditioners have benefits though. I really like Effol Hufsalbe (hoof ointment).
My horses are all shod front and back, and I apply the ointment all over the hoof wall. I have never had any problems with it around the nail holes. However, I always brush the hoof walls with a stiff bristle brush to make sure they are clean before applying the ointment. I think that is a really important step because you can trap the dirt and bacteria underneath the ointment and it will just keep building up and then that can lead to weakening the hoof walls.
On last thing, it can take about a year for the entire hoof to grow out, so it does take time to notice a difference in the hooves.