I hardly ever throw anything away and after years of that I realize it's not a moral issue, it's a practical one, and I'm a lot more harsh about what I decide to keep now than I used to be. Oddly enough, I have the remains of a Monogram Corsair that I built in the 60's that I have used as a paint mule, still on my shelf. That kit's mold has suffered a lot through the years and all the kits it has produced, the one I recently built with my grandson was not nearly as nice as the one from the 60's.
My advice is don't beat yourself up, if it makes you feel bad, toss it. However, I wonder if the skills I have, whatever they might be, are at a higher level now than they might have been if I hadn't suffered through some tough kits to a reaonable conclusion.