Yeah but then we also fall in the "and we throw the old one away" category. Sure, if we find the perfect one, we'll be sticking with it for a while, but if the new thing is actually better: stage pianos are tools, they're not precious instruments lovingly hand crafted by instrument makers. I will happily throw a Roland RD800 out the window if you give me an RD2000 instead. Same for a Nord Stage3 vs an old Nord Stage. Maybe if they were vintage, as pointed out somewhere else, but they're just not. There isn't a single modern stage piano that isn't just an excellent sampler with ideally a rock solid hardware UI. Zero reason to care about replacing those if the new model has better samples, or better hardware UI, or both.
The original Nord Stage is still an excellent instrument and commands high prices on the used market. There's no reason to throw the old one away and few reasons to buy the new one, because the old one does pretty much everything you need it to do.
We're talking about very mature technology. The difference between Nord's 100MB piano sample sets and a 20GB mega-multisample is extremely subtle. The synth and effects engine on the Nord Stage sounds fantastic. You could add a ton of sample memory and processing power, but the sonic benefits would be absolutely marginal.
