We know a good thing when we hear it!
Bottom line for me is, if you are happy enough with an arranger, you don't NEED to upgrade every 2-3 years..! I still don't understand how Yamaha manage to get their followers to drink the Kool-Aid every new model, especially with how little they add each time. What is it about them that leaves their users wanting change so badly? LOL
Fran's a 'buy to try' kind of guy (I think he's bought most of the Roland arrangers over the years), but me, I just wait and wait and wait until something comes out SO much better I absolutely must have it. Plenty of arrangers between the G1000 and the G70 (I missed the entire V/VA series) and quite a few between the G70 and the BK-9 (the Preludes and the GW-8 and the BK-5/3). I just bided my time.
I did get the BK-7m, but that was always intended as a sound source for my keytar rather than a serious arranger (although it has turned out to be very powerful, and possibly soon to be updated), but all in all, I tend to think that I only hear subtle improvements between adjacent models, and usually, you can go ten years or so before something SIGNIFICANTLY better comes out.
Just look at the Yamaha timeline, and imagine how MUCH better each arranger would be if you waited 8-10 years between models! You would have gone from the original Tyros to the T4! Or the PSR3000 to the PSR S950 - That's change you can believe in..!
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An arranger is just a tool. What matters is what you build with it..!