I attended a Porsche club event where one of the VPs for Haartz corp was in attendance. They make the canvas used in the Porsche top and have a factory in Acton, MA so he participates in some of the local events...
I was talking with him about the RaggTop (which he was handing out
) and their interior protectant product (yes, some of this too
) and you should have seen the look on his face when someone mentioned ScotchGard. Needless to say, they don't recommend it. They developed RaggTop specifically to let you get the best factory-like finish on the top fabric at home, and he said they spent a long time trying to get the results it now produces before releasing it and their other product. You can't tell it from a factory-new top IMO.
As far as wearing off, it is a coating - not something that becomes a permanent part of the top (ScotchGard in contrast probably does?), so it will wear off over time. I was just scrubbing too obsessively and taking it off faster than it would just wear over time. A spray rinse really does do the job and it lasts a long time under that care.