The modern world, as depicted by Wordsworth in “The World Is Too Much With Us,” may be increasingly prosperous, and it may provide us with more goods, more material objects to buy. But it is spiritually enervating, ultimately of no benefit to the soul. All this “getting and spending” may make us feel a little better for a short time—think of "retail therapy"—but ultimately, it brings us nothing more than a “sordid boon.”
What Wordsworth means by this is that the material benefits we derive from living in the modern world cannot compensate for the damage that rampant materialism has upon our souls. Material wealth may be a boon, but it is a sordid boon, utterly immoral, as it involves giving our hearts away to Mammon, wealth as an idol to be worshipped like a god.
Not only does this sordid boon separate us from ourselves, from our God-created souls, it also alienates us from Nature, which, to an arch-Romantic like Wordsworth, is nothing short of criminal.
We are an intrinsic part of the natural world, and yet, in our unhealthy obsession with acquiring money and material goods, we lose touch with that world, standing apart from the sea, the winds, the sleeping flowers, and all the other features of Nature.