The lea, on which the speaker is clearly standing, is the focal point from which his observations emanate in William Wordsworth's "The World Is Too Much with Us."  For, it is from this point that the controlling metaphor comes: the world with its debilitating system that limits the perceptions of the heart causes people to become "out of tune."  But, the sea and the winds seen from this lea can liberate people from their "world-weariness."  In Nature, people can free their spirits and open their consciousness of what is truly valuable in life:

...Great God!  I'd rather be
A Pagan suckled in a creed outworn;
So might I, standing on this pleasant lea,
Have glimpses that would make me less forlorn....

A Romantic who believed in the beauty and value of Nature, Wordsworth attacks the superficiality and conventionality promoted by the world that is absorbed in "getting and spending."  Indeed, Wordsworth's poem is yet very relevant today.

In my opinion, it is pretty clear that he is actually standing in the lea rather than being some other place and wishing he was in the lea.

The reason that I say this is because of the actual way he phrases the line.  He says "standing on this pleasant lea."  I think that the word "this" is what proves it.  It is not like he has been talking about a meadow up until now, so why would he say "this" if he were not actually there?

If he were not there, I would think he would say "standing on some pleasant lea" or something like that.