My trombone... 40 years!
The thing about GAS is, you are on to new gear before you have learned 50% about the gear you have..!
The thing is, something I notice particularly about arranger users is, it's the new styles and sounds that, TBH, 99% of us move on for. Few of us settle for long on one soundset (and many don't try too hard to convert newer and older styles to use the BEST sounds we have now).
And, given how few NEW styles and NEW sounds each of them tend to add, if you move from the last model to the latest, you gain very little. Admittedly, Yamaha make this easier for their users to do, having changed their OS very little for quite a long time, but Roland and Korg tend to concentrate on new FEATURES quite a bit, and Roland have this habit of trying to reinvent the wheel every new series, so moving to the latest, greatest involves considerable head scratching just to get back to the comfort zone they came from!
Me, I generally feel I need a piece of gear maybe 6 months to a year before I consider I have the same degree of command I have over the old one. Trouble is, if you turn your gear over every couple of years (that's the product cycle of most arrangers nowadays, especially the MOTL sector), you have maybe half of your entire use cycle not completely in control! For me, at least, that's not optimal.
One of the main reason I have stayed with Roland so long now is their Makeup Tools quick style and SMF editing tools. Each time I move on to another arranger, I am not content if I can simply PLAY older styles. I want them to use the best sounds, best kits, and to sound as close as possible to the new styles that came with the new toy. An editing tool that makes this feasible and easy to do is essential, or I end up with the majority of my show sounding pretty much IDENTICAL to how it sounded before. That's not a great improvement, is it?!
But, with boatloads of styles and sequences, even with great editing tools, it's not something I want to do every couple of years! Any time spent doing this is NOT spent learning new tunes, preparing new sequences, converting new styles...
So that, for those locked into wanting the latest every time it comes out, is why I don't do it. Pick a basic soundset that is great, punchy and versatile, what more do you need? A SLIGHTLY better sax sound? A SLIGHTLY bigger style selection? Until the arranger offers RADICAL improvement, what do you gain?
Not a whole lot, IMO...
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An arranger is just a tool. What matters is what you build with it..!