No last generation keyboard is better than next generation keyboard!

So, the progress will dictate you to change - if you choose not to, it's all fine of course!
What Korg did was very smart I believe - cut indeed features that were present in their previous middle range keyboard and were derived from the top line, but not essential for most of the users. In the same time, they reduce the cost significantly. Best thing for most of the users - not for all, but that made the difference between the TOTL nd MOTL much more obvious.

Fortunately, they did not cut the core features - sounds and styles. Quite opposite, Pa900 gives you actually something little extra.

Anyway, it's only you who can see the benefits for either changing or not. It is your playing, your keyboard, your money!