Caution against modifying the original saddle bone is not connected to the possible sale of the guitar in the future. It's because one can sand it down too low and then regret it. The thing is that the tone of the guitar after sanding the saddle down or replacing the saddle keeps changing for some time - several days or weeks. And it is possible that you may want to come back, if you will not like the tone or your new set of strings will start buzzing.
If you sanded down the original saddle bone, you cannot come back.
Most people are doing the way you do, however. So, not to worry too much.
Tusq saddle bones are wearing down, they do not last forewer. Look at these pics -
http://www.acousticguitarcommunity.c...ource=activity
Natural saddle bones presumably last forewer.
Enjoy your new ferrari!
