Well, this place is getting to the point of being useless to me now anyway, so I might as well just post uselessly in the sure knowledge that, as usual, no one will take away the correct conclusion.
Growth comes from this simple process: someone produces something that makes him some money, he then spends that money on what someone else local to him is making, and so on. In this way a small place with not much money, like say New Amsterdam in the 1600's, grows into a big place with scads of money, like say New York today.
It's the local part that counts: nations aren't the proper unit of economic analysis; cities are. New York City's economy is a separate and distinct thing from LA's, even if the two are, by way of sheer historical accident, part of the same nation. New York probably trades more with Philadelphia than it does with LA, and LA probably exchanges more goods and services with San Diego than it does with Chicago.
A city, or if you prefer, a region, since New York's economy takes in all of southeastern New York state, the northern half of NJ, Long Island, and Connecticut up to around Stamford, grows by producing stuff for itself, and exporting the surplus. The worst thing that can happen to a city is for it to have wild success exporting a single thing, like Detroit and cars, Rochester and photographic film, or Battle Creek and cereal. What happens then is that the entire economy becomes distorted around that single thing, and everything else withers. Cities that last and grow have a wide variety of exports.
"Investment", "consumption", "income", all that, are byproducts of the above. Statistics. They measure, but they don't explain. For growth to happen, you need a person with a good idea, the competence to see it through, the passion for the hard work it takes, and, finally, for all of that to take place in the context of a wider but local economy that will be open to buying what he produces and open to financing its growth if it takes off. Detroit wound up producing cars because New York bankers were skeptical of the industry, for instance. Fortunately they don't make dumb mistakes like that often enough to kill NYC's economy.
The crucial thing about investment, if you're going to obsess on that, is this: is the place you're looking at sucking up all the investment money that place produces and, ideally, more, or is it letting it go to other places? Detroit after WWII exported capital, a sure sign that its days of growth were over. Germany today does the same, and for the same reason: its businessmen don't see enough opportunity in Germany for all their investable funds, so they wind up using those funds elsewhere. Germany today is like Detroit in the fifties: it's wildly successful at exporting cars, AND it exports capital. If it keeps that up it will suffer the same fate as the Motor City.
Austerity and all the rest of that stupid nonsense don't figure in any of this because they don't count. What happened in the eurozone was a bunch of countries let go of their sovereignty, and wound up as economic colonies of Germany, the most powerful member of the club they formed. Anyone who's bothered to read and understand Jane Jacobs knew this would happen; watching it unfold has been both boring because it's so predictable and exasperating because of all the total bs you have to put up with, with people mouthing off as they, as usual, use current events to justify their preconceived notions that have precisely dick to do with what's actually happening in the real world.
The euro needs to go because it's the opposite of what Europe needs. Europe needs, and prospered, under a regime of multiple, local, and flexible currencies. It has predictably been laid low by a currency that is the precise opposite: single, continent-wide, and fixed. This has nothing to do with investment, consumption, taxes, or austerity: it's because all growth, like all politics, is local. But the world is dominated by careerists like the bureaucrats of Brussels who's interest is in making things as un-local as possible, economists who measure everything and can't explain a thing, and ideologues who know everything about nothing at all.