The syntax of the two sentences you quoted allows several possibilities for what "it" means. "It" could mean the money itself, money spent on advertising, a metonymic reference to the advertising, or even the entire first sentence. We need to look more closely at the content of the sentences to see whether what they mean matches any of these possibilities.
Here's a fuller quote from your link (emphasis, mine):
Money spent on advertising is money well spent. It assists a rapid distribution of goods at reasonable prices. It draws attention to new ideas and so helps enormously to raise standards of living. By helping to increase the demands of goods, it increases the number of workers needed to supply the goods and, therefore, provides employment. It helps to pay for many services. Without advertisements, your daily newspaper would cost a lot, the price of your television licence would need to be doubled, and travel by bus would cost more.
An important cue in relation to which noun a pronoun refers is the subject of the previous sentence. In this case, the subject is "money spent on advertising". It would be a natural 'first guess', but is far from conclusive. In my previous sentence, for example, "It" refers to "the subject" or "money spent on advertising" from the sentence before, but that sentence's subject is "this case". But in context, "this case" is not a "natural 'first guess'". A more important cue, then, is the primary focus of the previous sentence. If that focus is not immediately clear, use nearby sentences to help disambiguate, especially sentences within the same train of thought.
We now return to the extended quote. The context sounds odd if "it" was money. Money doesn't assist distribution at reasonable prices (put another way, paying more for the same advertising doesn't improve distribution at all); money doesn't draw attention to new ideas; etc.
Most clearly, though, the last sentence of the quoted paragraph refers explicitly to advertisements. The style of the paragraph strongly suggests that each sentence is talking about the same thing - each reference to "it" refers to the same idea. Hence the mention of advertisements in the last sentence as its main idea strongly suggests what it refers to in the previous sentences.
Looking at the content of the last two sentences confirms the suggestion that "it" refers to "advertising:
So I'd agree with you that in your quote, "it" refers to "advertising", not "money".