I would suggest that a lack of legal route knowledge will lead to an increase in illegal route use.

How can you aim for the legal routes, if they are kept quiet?

Having said that, I agree that you would very soon attract the non road legal riders, who you could assume would have the the same lack of respect for the rules of the non tarmac.

Either way, I know it's a flippin' pain in the bum finding good non tarmac riding!

(And family commitments keep me away from the local TRF meets).