The longer and more complex the contract, the greater the burden of enforcement by the state. Since long and impenetrable contracts impose a cost on the court system, they should be taxed.
If no "contract registration tax" is paid at the time the contract is signed, the contract should be considered null and void.
Contracts could still be kept secret under this scheme. Register the SHA256 hash of the contract, alongside its length in characters, in a government database.
One welcome effect of such a tax: You'd eliminate, or greatly abbreviate, those long EULAs whenever you sign up for an online service.
I don't think legalese is actually useful, I think it's just a bad habit.