In the context of the Martial Arts Companion and RMFRP, unarmed attacks are actually significantly better than armed ones with a main gauche. So a style that gives you two unarmed attacks is better than one that gives you two main gauche attacks, all else being equal. Is it enough of a bonus that it ought to be cost point in a combat style? Harder to say. Offensively, main gauche is not a very effective weapon, and the weapon styles charge you the same for any weapon regardless of its damage potential.
That said, it's the intent of the MAC rules that you could use an off-hand parrying weapon to get a DB bonus. There is the Defensive Ward ability (10 points) that lets you increase that existing DB by 10 or apply it to a second opponent. I think a weapon style with Defensive Ward and Additional Unarmed attack is consistent with those rules; you would get one weapon attack, one unarmed attack (to a maximum of degree 2), and your DB bonus from your off-hand sai/main gauche (plus 10 or applied to two foes).
I do think it's unlikely to have a style where you hold a defensive item in both hands and never strike with either of them. A fighting technique that depends 100% on kicks with no variation whatsoever is going to be a bit too predictable in my opinion. I certainly wouldn't give the defensive bonus for both main gauches.
