If you ask me, the root cause of the gelcoat chipping is poor lamination. Whatever process they use to make these things results in a weak part. If you look around at as many Gradys as you can, you see that these hatches, fishbox lids, bow pulpits, hardtops, etc are the first to go in terms of gelcoat wearing little more time, but the end result would be much stronger.
I think if my boat doesn't sell, I may pull my hatches off and use them to make molds. Then I'll lay up new hatches using gelcoat, epoxy and real glass. For the hardtop, I'm thinking about a piece of Aluminim trim to install around the edge to essentially cover up the chipping because I don't think I'll ever be able to fix it permanently. Kind of like the trim that was on the edge of the T-Top on my old 204.
If you want to repair the existing parts, my recommendation would be to start grinding the damaged areas and not stop until you reach solid laminate. Then layup new glass, fair and gelcoat. That's what I did to rebuild my front hatch...
Holes bored out and filled with epoxy. I also layed a few alternating layers of 3/4 oz. mat and 6 oz. cloth across the front edge to add strength.
Fairing compound applied over the entire part and then sanded.
Gelcoat sprayed w/ a Preval sprayer and then coated w/ PVA to ensure proper curing. I used generic white liquid gelcoat from Boater's World and tint it with brown coloring agent to get a near perfect color match. Even thought the gelcoat is already in liquid form, I still had to thin it w/ acetone to get it to spray properly.
PVA washed off.
Edges wet sanded with 400, 600 and finally 1500. Then masked off of non-skid application.
Non-skid applied and coated w/ PVA. This was also done with a Preval. Non-skid is done with gelcoat, it just didn't get thinned as much so it was slightly lumpy when I sprayed it. This creates a random splatter pattern that matches the existing non-skid. Then I sprayed a thin layer using thinned gelcoat to top it off.
Gelcoat cured, masking removed and hatch installed.
Duplicating the diamond non-skid is an entirely different process.
http://www.greatgrady.com/forum/viewtopic.php?t=1281
Hope this helps.