hell yes. empty time is absolutely valuable in and of itself. I know this, I’ve known it for a while, and I still have the same problem you describe: I don’t make myself do it enough.
I wrote about this a while ago: https://snarfed.org/2012-01-16_coffee_breaks_for_the_brain , and I’ve been planning the same unplug day per week idea, or at last half day, but for a different reason: we just had our first kid. I initially thought of it as a good thing to do with her, mostly when she’s older, but maybe it’ll be just as good for me.