On the topic of noticing performance improvements, I'd definitely say that we've plateaued as far as "general snappyness" in all aspects but one: high-refresh rate, low latency displays.

I recently upgraded my monitor from a Dell U3014 to an OMEN 27i (it's gaudy and "gamer" oriented, but it was the best I could get in an afternoon at a physical store). That's an upgrade from a 60 Hz monitor to a 165 Hz monitor, and a significant (though not numerically measured so far) drop in input delay, some tens-of-milliseconds.

This has been the biggest improvement in "snappyness" that I've experienced since I moved to solid-state storage 10 years ago.