Charlie,
Since you own the R3 you may be underwhelmed. I'm on the other hand intrigued as I do not own a high res body. In reality if Sony rolls out with an A9mk2 with 30MP sensor body that would be much more logical for me. I wouldn't complain picking up a current A9 mk1 TBH.
I'm still analyzing my uses for a high MP body. 30MP is more of a sweet spot for my application.
the flexibility of 60mp is certainly nice, just not nice enough for me to plunk out 1500+ to do the upgrade (assuming I can sell my old cam for 2k).
it's not all about the pixels, I upgraded from the R2 to R3, took a bath, and well worth it IMO. The body adjustments were huge for their time. The camera much faster, battery more than doubled, joystick touch screen, custom functions, etc.
The problem with this R4 is that all those previously very important weaknesses have been addressed, so the R4 had to improve on stuff, and outside the pixels, additional sealing, I'm just not seeing much that warrants the upgrade..... however if you're shooting 24mp and want something much higher..... this will hit the spot. Either way, usability is a bit lacking with this upgrade, and thats an area I'de like to see Sony tackle more. They're doing that with this R4, just not enough. Less or no blackout, better touch screen experience, A9 like UI, which has improved a lot? (might be there already).
The top dials like the A9...... what gives? Why cant all the models get that? They're friggin dials, and it's still a 3500 dollar camera. It just bothers me when going from the 7 to 9, when they're essentially the same form factor. Hate fiddling with stuff when I get disoriented. Thankfully, I'm using the R3 mainly for very still life, and video, not a big deal, would love to have a 61mp body, but I'm asking for more than megapixels 
here's a video of the difference which should be really bug fixes that come in firmware updates....





