I've used shoe goo to get more life out of shoes. It's marketed as an adhesive, but you can apply it to the bottom of the sole to rebuild thickness to the tread. A single tube could be used for dozens of repairs. After that for me, usually the textiles in the upper fray from the inside out, and I just ignore it until it becomes externally visible or uncomfortable.

I don't think more extensive repairs are economical, and you are better off wearing shoes you like until they disintegrate. There is a bit of mythology about buying expensive boots and repairing them in the hope that it's more economical, but it's really not: https://mastodon.social/@danluu/111068432320682422