I think everyone buys an arranger for his own reasons...
I as a currently not performing musician (I play music as a stressreleave from a stressfull dayjob) buy a new instrument as a new tool to toy around with and to explore my limits with that tool....
I will never reach an instruments limits, but playing on a new tool makes things feel fresh and challenges me to do different and new things.
And so everyone has its own reasons to buy or not to buy a new instrument.
With all current topmodels having top knotch quallity sounds, its features and interesting ways to toy around with music and sounds that make me buy a new instrument.
I think yamaha and Ketron that espescially create instruments to be played straight from the box would not so be my choice. 
I prefer the ideas behind Korg, General Music but new ways of creating music like the possibilities of Linontracs (Q-ranger/vst's) but also arpegiators combined with arangers and espescially KARMA are luring me intoo buying new tools. 
I am on the verge of discovering new ways to play music and spread my wings beyoud just playing Arranger styles or playing piano style along with midi/audio. 
Not being dependent on these instruments for gigging gives me total freedom of switching instruments, but if i was dependent on my instruments for supporting my familly, i'd have a different attitude.
With current soundquallity and possibilities I can't think of a reason to leave great instruments like G70, Tyros2, PA1X for something new.....these instruments sound great in the hands of a capable musician and no one in the audiance will probably hear the difference between a T2 or T3, so why rebuild my whole setups and put tons of money in a new instrument when none notice it?
All i want is to have fun doing so while realising that i will never ever push these great instruments to their limits.