1. I do not save the zip files.
2. I will usually use the kit at least once, but there are some I turn to again and again.
3. I remove kits/products when I no longer feel like they fit my style or will be used. Even if I've never used them.
4. If I will use a product, I keep it whether it's retired or the designer is retired. I have things that are old, but the product still does what I need it to do.