'm sure there will be many of these comparison videos to watch, but here is a look at the HX vs Agoura Deluxe Reverb (vibrato) amp model:
Playing the two models side by side, you can definitely feel/hear a difference. But you have to be able to A/B between them quickly in the exact same listening environment. You'd be VERY hard pressed to hear a tone in a mix, or sit down and play something without knowing what it is, and say, "Yes that's an Agoura amp model, and not an HX model".
That said, I definitely heard and felt what I would describe as a significant improvement.
It's interesting how people attribute fizz to 'digital' (or 'digital harshness'). Having captured close to 100 real amps with mics on cabs, there is often a LOT of fizz that you hear in real amps, and things like mic choice, placement, speakers, post-EQ, compression, etc have a huge impact on how much fizz you hear, or how harsh it is.
That said, I find the Agoura Deluxe model to be much less 'fizzy'.