I find it infinitely more resourceful to have a well-stocked kitchen with ingredients that last a good while than to go out and buy a single serving of anything. I would never consider buying a specific spice or sauce "an investment" in a single type of dish given both the small cost and the viability of those items in other types of cooking. Hoisin is great when making hamburgers or chilis, for example.
And while that doesn't sound like much, again, when we're talking about buying a completely new set of sauces to make one dish, it's $3-4 multiplied by the 5 new sauces and condiments to be closer to $15-$20.
And yes, if I use those ingredients regularly, then they quickly pay for themselves, as the Hoisin sauce lasts like 20 meals and the price per serving becomes fifteen cents a meal. But at the outset, if I decide I want to try Orange Chicken and it costs $20 + the cost of meat just to get the ingredient set, it's alot cheaper just to pay $11 and order some from a Chinese restaurant, no? If I like it, great, I can make it again. But if not, I've spent more money than I needed to and am left with five bottles of sauces I'll never use again.
Case in point: I've got a recipe next week that calls for "dark soy sauce". I have no clue WTF that is or if it is sufficiently different in taste or texture that I can't just substitute my regular soy sauce in for the recipe.
One thing it does well is providing only as much of said ingredient as you need. I recently tried to get into Chinese cooking, and before I made my first two or three dishes I had to run out and buy Hoisin sauce, chili garlic sauce, oyster sauce, Chinese rice wine, and minced ginger. That's quite a bit of an initial investment before I even decide whether I like the food or not. So if I can pay a little extra upfront just to get whatever amount of those sauces I need while I'm still in the trial phase, that would be nice.
As someone else said, local grocery stores could probably do very well just by providing their own meal kits. Wegmans does this on occasion, although their stuff is usually assembled to the point where you simply bake it.