I've only gotten to play on a BK5. I thought the styles were quite good, but other than piano, organ and elec piano, I didn't find any sounds I liked. I guess the BK 9 is a different animal though.
Actually, the Piano, Electric Piano and B3 organ are VASTLY improved on the BK-9! If you thought they were good before, oh my! You have a pleasant surprise in store. And there are about 600+ more sounds in the BK-9 than in the BK-5 and about 17 more kits.
It isn't simply a beefed up BK-5. It's quite a different beast.
TBH, after several weeks on the BK-9, I am getting used to the screens. Most of what you need to access on a gig is easy to set up on the 4 switches by the bend lever and the FC-7 as far as functions go, and numeric and Favorite sounds, styles and Performances make quick recall if you are doing free panel. Mind you, who is still doing things that way? Set up the Performances into Songbook style, and things are easy to run.
And the FULL Performance editor and other handy iPad apps is starting to make the touch screen not as big an issue as it was when first released. As usual, Roland tend to let something out into the wild before it is quite finished, but the new OS and the BK-9 Performance editor has narrowed the gap to my G70 considerably. I'm going to be testing the BK-9 editor on a borrowed iPad soon, and I'll let you know it it can substitute for the touch screen.
Don't forget, a BK-9 and an iPad is STILL quite a bit cheaper than the G70 was..!