I thought the object of investment DID matter?
Not as far as the stimulus is concerned.
For instance, just spending money on ditch digging would result in a whole bunch of holes, which could create its own set of problems economically. Best examples I can think of is world fair areas or Olympic parks. How many of these parks actually benefit the countries long term?
But the stimulus isn't long term.
The whole point of the stimulus is to get money moving that otherwise wouldn't be moving.
The best thing we could do for the entire economy is for everyone to go out and spend 20% of their savings tomorrow. On anything, it doesn't matter what. All of a sudden, everyone would see their sales jump, stores would see their inventories drop dramatically, suppliers would get orders to restock those inventories and have to increase production, people would have jobs working for those suppliers, and the economy would be running again.
But I'm not going to go out and deplete my savings tomorrow if I don't know that I'll have a job in a month; I may need that money to live on. But that means that I'm
not buying stuff, that stores are sitting on unsold inventory, that suppliers are seeing reduced orders and cutting back, and people are being laid off.
It's the "paradox of thrift." A high level of consumer spending in this situation is a classic example of a public good that the market won't deliver because each individual actor wants to maximize their own utility, not the utility of the economy as a whole.
So, if I can give the twenty million Americans without jobs something to do -- even digging holes, or canning bicycles in syrup -- then they'll be willing to spend their savings accounts. That's the idea behind the stimulus. And once they're spending, companies will start wanting to hire them to do other things than dig holes and I won't need to pay to have as many holes dug.
However, investment into things that have both the stimulating advantage AND a real use (e.g., infrastructure, new useful technology, education...) is when you will see a great benefit.
You will see the stimulus benefit from simply putting people to work and getting them spending. But as long as you need to put them to work, you might as well get them to work on something useful. The stimulus would still work if people were canning bicycles, but they might just as well build a high-speed rail link that will reduce the costs of doing business instead.