Learn English – What does “…,what foul dust floated in the wake of his dreams that…” mean

It means that not only the headline annual economic growth numbers of China are important to the rest of the world - China's other monthly economic data is important to the rest of the world too.

China's annual economic growth numbers and other monthly economic data are all important to the rest of the world.

China's annual economic growth numbers are important to the rest of the world and so are China's other monthly economic data.

In the sentence, it does not refer to Washington. So, you shouldn't be interpreting the sentence in this way:

✘ I've been to Washington several times, and I like (Washington) there.

Instead, it is a dummy pronoun. From Wikipedia:

A dummy pronoun, also called an expletive pronoun or pleonastic pronoun, is a pronoun used to fulfill the syntactical requirements without providing explicit meaning.

In the sentence, it does have some meaning, but it's not exactly defined. For a native speaker, the meaning of the sentence is generally the same as:

✔ I've been to Washington several times, and I like (something that exists) there.

A conversation could go something like this:

"I've been to Washington, and I like it there."
"Oh, really? What's there that you like?"

The use if it is non-specific. It refers to something, but the sentence doesn't clarify what it is. However, it does say that it exists there in Washington.

There is also a contrast between here and there (and anywhere else):

I hate (the weather) here in Antarctica, but I like (it) there in Washington.

The use of (it) has changed from a dummy pronoun to a referential pronoun because the first part of the sentence has actually made it clear what (it) is that's being referenced. But the important part is the contrast between here and there.

Compare this with the sentence in which there has been omitted:

I've been to Washington several times, and I like it.

In this sentence, no dummy pronoun is used. It is a referential pronoun that refers to Washington.

Although awkward, the sentence could be rephrased in the following way:

I've been to Washington several times, and I like Washington.

A similar conversation could be constructed around this:

"I've been to Washington, and I like it."
"Oh, really? What do you like about Washington?"

Note the specific difference between this conversation and the earlier one.

Whereas it in the first conversation refers to something completely undefined (aside from its existence in Washington), it in this conversation refers to something about Washington itself.