I find you can taste the quality difference when making a marinara sauce, tomato soup or pizza sauce where tomatoes are the star of the show (e.g., a neopolitan style pizza especially a margherita) -- but if the sauce is secondary you can't really tell and it's not worth the added price (e.g., meat sauce, pizza loaded with other toppings).

We'll use San Marzanos for homemade marina sauce and homemade pizza sauce (because we make a lot of margherita pizzas) but if we're making something like chili we'll get the lower grade stuff.