Common approach.
Jim: One of the common approaches to this problem is to use a can opener (aka Church Key). Use the tip of the of the opener to scratch out the crack which will create a small groove. Then you can fill the crack with something like Marine Tex or an epoxy material. I would assume that you could also use a dremmel type tool too. You probably want to make sure that you do not go too deep. Once you have patched the area you could then use a gel coat kit to touch up the areas. Also check out the West Systems site. I believe that they have some instructions on such repairs. Are most of these spider cracks in areas where there are curves (like the cockpit area)? If they are really small you could also try Captn. Tolleys crack creep. This would seal the area and you should not need to worry about the touch up of the gel coat. You could just wet/dry sand it after the cracks are sealed up.
