I think the one reason I'd hang on to an SX900 if I were a guitarist is the Chord Sequencer.
To be able to have interactive backing that I could still control simply on the fly without having to play the chords seems like a good thing! Set up different sequences for Verse, Chorus, Bridge etc., and you could be playing guitar and still pretty easily selecting what section you want to do on the fly...
I had been underwhelmed by the last few generations of 'baby steps' improvements in Yamaha's arrangers, but I must admit, the SX900 is the hugest leap forward in decades for their model line!
_________________________
An arranger is just a tool. What matters is what you build with it..!