I've been fighting with the automatic accumulation of downloads for years now - it really makes it impossible to figure out if whatever I downloaded can safely be deleted - so my current system is similar to the OP's one, but a little gentler: I have a launchd task that runs every day and warns "I'm about to delete these things that are older than two weeks", which lets me salvage anything I might have forgotten to archive.

Source here in case it's useful for anyone: https://github.com/f-f/home/blob/ee0ae5dd201ac6e8ffa60fff71b...