If you go back to the Signature Edition you had fewer memory banks, though you can still get an upgrade. The earlier Performer series when first sold years ago had fewer memories compared to today.
As suspected, the various editions and price differences just involve wood and lighting.
The operating system can be updated via MIDI so there aren't any OS changes that require service. Earlier units had poor aftertouch generation from the keyboard and can be upgraded.
Obviously the Old School and new XL unit have substantially different hardware, but not the other editions.