Taking my Pickled Ginger garnish suggestion one step further I would also suggest adding Soy Sauce as either a dip or a garnish.
Placing a nigiri card on top of Soy Sauce card would be dipping or placing a Soy Sauce card on top of a nagiri card would be garnishing. In each case the Soy Sauce would score up to triple the nigiri card points.
A nigiri card could not be both dipped and garnished with Soy Sauce.
A further argument could be made that a nigiri card can only be dipped or garnished once by any ingredient.
Perhaps these ideas could be considered for stretch rewards or possible future expansions.