"A Keyboardist should NEVER sacrifice Sounds for features." Never say "never". It depends on what else you might have.

Sounds and polyphony are easily supplemented with a module. It is harder to deal with inadequate style storage, poor chord recognition, lack of vocal harmony, slow transfer rates, lack of continuous controllers including aftertouch, a bad navigation system.

Also, Korg is criticized since its cards do not add polyphony while Yamaha's do. On the other hand, Korg's 62-note polyphony applies to the added sounds as well as the original sounds. In the case of Yamaha, the added sounds have only their own polyphony and do not benefit from the keyboards base polyphony. For example, Yamaha's VL voices have 1-voice polyphony, period. Also, the added polyphony is not available to the original voices. Basically, Yamaha allows you to have 2,3, or 4 synths in one case, but integration of these synths is limited.