Glad I doubled the RAM in my Mac mini to 16GiB, but also horrified that I'm using a lot more than 8GiB. This means I was exceeding the available RAM before the upgrade, and that most likely explains why the system stopped being particularly responsive at times.
Anyways. Any future upgrade will be to a Mac mini that can take more than 16GiB of RAM. One of those snazzy 2018 models, for instance.