Sound... Admittedly, I haven't heard a BK-5, but I have a BK-7, and it can sound as good as a PA3x for much of the styles. Amazingly live sounding drums, fat bass, great pianos, far better guitars than my G70...

PA500 is still older technology, PA2 era or earlier, right? 80 voices as opposed to 128. Older sounds and no guitar modes, right? Pads, yes... Roland need to wake up and smell the coffee. But who is doing serious sequencing in an arranger these days? You use a DAW and transfer the file... But the BK-5 has the Roland's typically first class editing tools to fine tune the sequence or style, something still not as well developed on Korg's (and WAY important, IMO).

And people not being satisfied with what they have has taken us from the plains of Africa to our modern lifestyles, health and longevity. Since when was that ever a BAD thing?!