Well, I can see the benefit of using substitutes, especially when someone is "trying out" vegetarianism, for example they start to eat one vegetarian meal each day, or even once they finally become 100% vegetarian. For one thing, the mind can't think of so many new concoctions, substitutes are easy, etc. They have their place.
But I think eventually people should perceive the vegetable kingdom as an entree on its own, there are certainly a many dishes out there that stand on their own, and are not "mock tuna" "veggie burgers" or whatever. Plus I do find eating large amounts (slabs) of soy and/or wheat gluten not the best choice for optimal health (in the long run).