I have to say that there has been no discernible difference in the tone of the various Wals I've had... not to my ears anyway.
It's my belief that its the pickups that are responsible for that unmistakable tone. There is more to a build than tone obviously and Wals have the balance, looks and playability of a top quality instrument, but it's really the sound that Wal players are buying into.
I am a huge Wal fan and for me they are the best bases I have ever played and I have little intention of playing anything else in projects where I have free reign over my tone.... but in truth I think the finishes are mostly a cosmetic choice.