One of the reasons that I went to Lexus was that the depreciation on them is so good. I originally bought a new 300H in 2017 and intended to keep it for a while. However, when it went in for it's first MOT in 2020 I got a new facelift version because I was made an offer that I couldn't refuse. With the warranty extensions every year, I probably won't change mine for another couple of years at least.
I haven't driven the 450H, but I have driven the 350H as a courtesy car whilst mine has been in for service. I'd say that it is a slightly improved interior than the 350H, with the biggest benefit being the fact that the infotainment control is touchscreen rather than the extremely clunky touchpad. By far the worst thing about the 350H (apart from the canbus theft issue) is the terrible software. However, I virtually never see it because I use CarPlay all the time (and invested in a dongle to convert it to Wireless CarPlay which is a game changer in my opinion).
The ride quality seemed similar between the two, in my opinion. Lexus seats in general are probably the most comfortable I've ever had in a car and the comfort generally has been commented on by people in the car.
I'd recommend checking out the cost to insure the 350H vs the others as well. The theft of them has pushed premiums up and there are many comments I've seen here and elsewhere from people who just can't get insurance in their area. Although a fix has been promised for some time, I'm not holding my breath on it. The tracker doesn't resolve the fundamental issue, and doesn't seem to make any difference to my quotes.