There are a lot of references to nature in "The World is too Much with Us"; the speaker refers to the sea twice, he describes a lea at another point, and he also talks about the winds. But the poem isn't so much a celebration of nature as it is a lament about the state of man's relationship to it. While the poem doesn't critique mankind's destruction of nature per se, the fact that people are no longer moved by the natural world makes it figuratively dead.
The speaker is just like those he criticizes in that he too is no longer moved by nature; he would rather be a pagan because nature would then have the power to move him.
The beauty of nature isn't "real"; it all depends on our perception of it.