The PSR8000, in my opinion, remains one of the all-time best Yamahas. Sure, the later ones have an improved OS, but the 8000 had some really neat features that have been discontinued.
It had the Groove function, which allowed you to easily change the timing on styles and save them in a special bank, effectively doubling the number of styles. It let you arrange the factory styles in banks of your choice.
By using the four style assignment buttons, you could effectively increase the variations, intros and endings to four per style.
It had aftertouch. The vocal harmony and voice processor was BETTER than the 9000, at least to me. Unlike the 2000, the harmony presets worked as they should.
It was built to last, other than the infamous keybed strip, which is easily replaced.
The registration system worked better and easier than the newer ones. You had dedicated bank buttons that let you quickly call up any registrations without going into a different screen.
There was more control over the style parts in real time, with wheels that adjusted the individual part volumes, instead of having to go into the mixer.
If I had to choose, of course I'd choose the 3000, but it's not a no-brainer, especially if the 8000 is in good shape and you can save considerable money. I went back to the 8000 twice after "upgrading" to newer models, and I kept it as a reliable backup up for several years after that.