I personally try to mask as many stars as possible. The bigger ones are generally more susceptible to being destroyed via processing than the smaller dimmer ones. Masking the medium to bright ones is more important than the little ones.
I usually create a star mask for the linear processing and then another one after it has been stretched and then use a Max() function on both of those to pick up some of the stars that are easier in stretched and un-stretched images.
When actually stretching however, you don't want a mask active at the time. Try it and see what it does
