That would likely slow things down because everything that needs to be written would no longer get written on a fast SSD, but on a slow HDD. Reads would be fast as expected (unless it is accessing something that has changed and is now on the HDD), but any writes would be quite slow. In my personal opinion, this wastes the potential of the SSD (like people who store /tmp or swap on an HDD, when those would benefit highly from the increased SSD speed).

And extending the life of the SSD is a largely pointless endeavor on modern SSDs. They'll write more data than most users could ever imagine to write before the NAND fails due to excessive writing (we're talking almost 5 years of writing 400GB every day to the drive -- and that's just for the first drive that failed).

Final update - Having Eric's and bassmadrigal's comments ringing in my head "eventually something will break using -current and an older KTOWN", plus recognizing that I don't really have the time to always be trouble shooting issues that might pop up with -current (like the days lost in December from libinput and February setting up manual updates"... I've moved back to 14.2 with base KDE and will stay there with sbotools and slackpkg updating. I have an eye on Eric's blog for updates to qt5, openjre, and VLC. This will be my working configuration rather than as stated in post 1. Cheers all.