aghhhh.... i feel for you.

if large areas of fiberglass needs to be removed, heat from a heat gun is a common way to do that.  but i don't have experience doing it on a stitch and glue.....just on a strip-built where you don't have to worry about post-glass-removal-sanding going through the veneer.

if i get your concern, this is a bright finish (see through/varnished) and that's the look you want to preserve.  so its not just removing the fiberglass, but not screwing up the veneer of the plywood underneath.

i know the folks at CLC routinely completely refinish their boats....so i am curious what they might suggest.

my only other two thoughts are -

1) have you rubbed the area down with denatured alcohol - if you do that and the result is transparent/looks just fine, then you are actually ok..   once the alcohol evaportes, you can simply recoat with epoxy and you should get the same look as when the alcohol was on it.

2) you can always consider painting.

 I have read about using a heat gun to remove fiberglass but its an area about 6" x 9" making it difficult to control the heat in the surrounding area.  I have not tried the denatured alcohol.  

Before I started refinishing, I could actually feel the surface of the cloth in the areas where the remover penetrated too deep.  I've since applied two layers of resin over the area and the cloth is still showing through.  

The deck is sapple with a dark rich brown grain that I definitely want to retrieve.  There are two layers of glass in this area so I am thinking of taping off the area and mechanical scraping with my carbide scraper to remover the top layer of glass.  I can then light sand and apply and new layer.

Thanks for your input.  As they say "haste makes waste"

I may give the guys a CLC a call today for some ideas and bouce this idea off them