I’ve owned the Nordost QX4 and QB8 together with Frey 2 cabling and it added a vibrancy and 'your are there' perception to my system. A few times my wife and I had our kids turn the QX4 off and in a blind test and we both heard the difference 10/10 times. It is very expensive for a return that you might get with component upgraded depending on what you have now..
Haven’t tried fuses yet. I trade a fair bit of gear as part of the journey so to drop a few hundred on fuses after a few hundred on tubes for something that I have a 70 percent chance of selling....That said I have excellent synergy now so I might, if I decide the synergy is more fun than the adventure.
I question your post placement btw, perfect place to bring up fuses?