I've had mixed results with the whole starchy water thing. I think it also depends on how much water you are boiling the pasta with in the first place. Perhaps you need to intentionally use a lesser amount of water to cook it in so it's not too diluted to make a "sauce" with it. I've tried similar recipes, though not meat and dairy free, that suggested a dish such as Orichette with Broccoli Rabe and Sausage only needed some starchy pasta water and some parmesan cheese to form the pan "sauce". I either wound up with a watery puddle on my plate and none of it was coating the pasta or the pasta dish was bone dry, so I ended up dressing it with some extra olive oil.
Incidentally, if you simply want to make a pan sauce for pasta that is dairy and meat free, you could just use margarine for the butter, and a golden vegetable stock for the chicken broth, along with the usual stuff like shallots, herbs and wine - plus maybe a hit of lemon juice.
Whole Food's make's a pretty good store brand vegetable stock, their "365" brand, which looks and sort of tastes like chicken stock. Some veggie stocks can be very tomato-ey and a reddish brown, while some others are also a brownish color and have a mushroom-y taste to them.