2. It's not depletion so much - you can always add food - it is the buildup of diseases.
Tomatoes, by the end of the season, can typically suffer from bacterial, tomato spotted, verticillium or Fusarium wilts - spread by fungal spores or insects chewing on the leaves - and that works itself into the soil. And there is no way to fight the bacterial, viral or fungal agent that causes these afflictions.
So I just dump it all into a pile and use it for other pots (greens, flowers, herbs) or in my garden beds.
It isn't a guarantee there would be issues, but certainly a likelihood....I also bleach the pots each year before using them just to be sure.