Fortunately, that is the case, and to the extend that it is true, I don't object to them, all that much. I just doubt their ability to stimulate. In other words, if you need a road and you build a road, then you end up paying for a road and getting one, and that's it. I question whether the act of building a road will somehow stimulate a great deal of other activity that would not have been stimulated.
To the question of whether infrastructure spending stimulates the economy, the answer is clear. If you build a road to a town/city/island/whatever, you are opening up routes for shippping goods in an area where you would have been previously unable to do so. As a localized example, before bridges were built to Clearwater Beach, moving goods/services/people to the island could only be done by boat. As the first bridge was constructed, commercial freights, plummers, electricians, tourists, etc.. could easily travel to the island, and facilitate the growth which now enables Clearwater Beach to be the most recognizable icon of the city, and the most profitable. Moving into a macro-view, having something such as the interstate system facilitated interstate travel to all areas of the country, and having the same effects on a national scale. As a historical example, when rail lines were first brought to the midwest (or west back then) in the 18th century, the economic impact of more farmland, more people, and need for goods and services to support those people, was enormous -- without infrastructure expansions, the odds that you would be living today in Michigan is quite small.
Now, obviously there are diminishing returns to infrastructure expansions. The fifth and sixth bridge to Clearwater Beach will not yield the same results as the first or second, because there is already access to the market. This is why I have used infrastructure as something that was used in the past as an example of stimulus, while at the same time do not advocate expanding infrastructure now as a stimulus for the present.
I could, however, see investing in energy as a present day possibility. By reducing the need for importing oil, you would see long-term GDP impact because improving export/import ratios positively influence GDP growth. Also, if a given technology were developed here and was able to be exported, the ratio would move even faster, shifting to more exports and less imports in that sector. Investing stimulus money here also brings jobs (some of which will be sustainable, because someone must remain to maintain the facilities after a plant is built), and increased production because the facilities need to be built and technologies developed.
Sure, the specific spending of money will be modified, but I question whether the "stimulated" spending isn't just a shift from one spot to another.
The likelihood is that it will not. This is because you are spending more than you are taking in (borrowing) to pay for the stimulus. If you were to increase taxes to pay for the stimulus, your above statement would probably be true, and, in fact, it would not be a shift but a reduction. This is because of inefficient lags of government, which must pay to collect, decide, and distribute the money, so not all of what was originally taxed would make it to stimulus.
It's a bit like publicly subsidized sports stadiums. They are justified by saying that the existence of the stadium brings in all sorts of business, and look at all that tax revenue those businesses generate. However, does it really increase entertainment spending, or does it tend to concentrate that spending in a particular locale?
I don't know if this analogy is apt, especially concerning borrowing to pay for spending as opposed to taxing to pay for it. What city governments will say, however, is that building the sports stadium will benefit consumption and investment for future decades. This is a bit off-topic, but I disagree with your analogy.
No one keeps currency under their mattress anymore. Therefore, all the money used to buy bonds would have been used for something else if the bonds weren't available. In other words, if the US magically balanced its budget, paid off its debt, and had no need to sell bonds, then a person who bought a savings bond or a T-Bill would have to do something else with that money. He might spend it, in which case it would go into the C part of GDP, or he might invest it in a private company, in which case it goes into I, or he might put it in a bank, in which case it facilitates lending for consumer goods or business loans, increasing both C and I.
However, since there's this safe, low risk, investment, it goes to the government to help pay its bills.
Ah, I see what you're saying now, thanks for expaining it in further detail.