Ian, I have played the Tyros 4 on two occasions, each time for about two hours, thanks to Don Patterson in Lufkin, TX.
I am very impressed with it, particularly the lead sounds and the new vocal harmonizer.
Is it the best one to suit me? Not sure. I still like the more raw sound of Ketron and Roland a lot.
Drawbacks, for me: It is larger than it needs to be. The new drum kit is nice, but many of the styles still use the older ones. Yes, I know they are easily swapped.
I believe it does sound better than previous models, but does the audience know the difference? Maybe a few, but most don't care.
I don't do a lot of big production songs that sound like a 20-piece orchestra. I want to sound like a small live band or combo. I never layer more than two voices, and usually only play one lead voice at a time. I seldom use a left-hand pad-type sound. My lead voice choices are guitars, piano, saxes, organ, harmonica, accordion, fiddle, vibes, and occasionally EP, trumpet, horns, vocal and gimmick special effect sounds. All those are well-represented on Tyros, but then they are on everything, some better some worse.
As you say, it is inspiring to sit and play, but then I am still discovering things on my old keyboards that are new and inspiring, if I take the time to dig into them.
I like a lot of things Yamaha does that nobody much mentions, such as multipads, short cuts such as key combinations that instantly mute everything but drums and/or bass, direct access
shortcuts, intuitive fills and breaks, text display, ease of USB use, double push endings for ritard, and other things I'm forgetting.
I'm not a big fan of the Registration system. I prefer the Roland and Audya (not the older Ketron) systems. Roland and Korg also have better music finder (songbook) systems. (Ketron has NONE). I don't like the big, bulky optional Yamaha foot controller. It weighs as much as some keyboards. Ketron has choice of several and Roland's is also smaller and works great. I forget about Korg, but theirs is smaller too.
Probably one of the biggest drawback for me is the unorthodox size and shape, particularly for a 61-note keyboard. It's even hard to find a case that fits it. As with all of them, there are great features and drawbacks. We each must choose what suits as best.
Anyway, like I said, it's GREAT to have so many good choices now.
DonM