I have a same feeling! Exactly same. 4th gear vibrates at very light pressure from my hand. And especially when you push the gas or applies engine brakes, you can feel the click. I think this is normal as you have a same feeling with my 2017 wrx limited.+1
I bought both within a couple months of owning the car, and they helped clean up the shifter feel immensely. The shifter stop is an easier install than the bushing, but the bushing is easy itself as well. Hardest part to is removing the cover plate to reach the bushing.
One thing I have noticed, which I don't know the cause of, if the shifter seems to vibrate oddly in fourth gear when i'm resting my hand on it. apply enough pressure, or let go completely, and the shifter sits still. But once I put a minor amount of weight against it in 4th gear, it starts to vibrate. Has anyone else noticed this?