I just bought a used MZ-X500 - about $950 including freight and tax.
As a Casio PX-560 owner, the MZ-X500 will replace my WK-7500 for compatibility sake. Two keyboards with a similar display and user-interface should improve productivity and creativity. The WK-7500 has been idle for many years and it's time to move forward.
As a semi-retired person, there's more time for musical exploration and composing. My biggest obstacle, as an older person, is that technology has surpassed me and it's difficult keeping up. I will seek all the MZ-X500 tutorials that I can find to maximize my purchase.
Feel free to reply with ideas or suggestions.