I think it depends that you're reusing them for. I bought some of those "Stasher" branded reusable plastic bags for lunch things, they got gross pretty quickly, hard to wash, and then they started coming apart at the seems. Pretty dumb optimization, considering they cost $15 for three bags. My grocery bags, though, for loading up at the store are good, and last a long time.
As in all things, moderation, do the 80% etc...