i had similar wear on the bottom of my nacra hulls

fortunately nothing had been done to them so i was able to clean them up nicely with 2 thick gel coat mixes brushed on with a paint brush, not perfectly fair but i don't race

if you've got a previous epoxy bottom job already on your hulls then you are probably best to continue with epoxy

something in epoxy inhibits the catalytic reaction in gelcoat, polyester resin, so it just stays tacky and either never sets or sets so weak that it peels off in next to no time

for your daggerboards, just clean them up with sandpaper and then give the bases a couple of coats of white gelcoat

for the leading edge chips/holes you could just fill them with 5minute araldite, or drip some white gelcoat in there a few times