Well I've just had a grand night, with my Tea Chest Bass and occasional washboard.
I play a "real" washboard, zinc and well used. The pitch is perfect. I have yet to see a washboard for sale that has close enough pitch. The modern "copies" go "ratta ta ta" not "Brrrrr".
Cajun Washboards are a different instrument to a true washboard. Typically American, all show and fuss but no depth. I have augmented my board with a few well chosen extras and it's a fun instrument.
Like all percussion instruments on the folk scene, little and subtle is the key to acceptance, loud bodhran, loud bones, loud washboard or even loud saw, are not good. But sensitively handled they can enliven an evening
I rest my case.

Ni Ni,

Andy