I doubt seriously anyone is paying the "big price tag" If they are....Can't blame Yamaha for that. The question is or should be "What is the Tyros 4 worth?"

and that answer depends on what board one currently has...

For a T3 owner it has to be worth $1500 more.
For a 910 owner add another $1000 or so to that.

For a Roland or Korg owner.....$100 may not do the trick. Those 15 extra keys are very valuable and necessary to an income