A couple issues: 1) It's true that higher savings leads to faster growth, 
but only in the short run. Let's assume that the classical model is 
correct, which Keynes didn't, and that equilibrium in the loanable funds 
market through adjustments of real interest rates leads to investment  
equal to savings. So an increase in savings will lead to an increase 
in investment and spending by firms for new capital. But this will not 
continue indefinitely. Capital wears out and so capital stock will adjust 
itself to the point where savings equal depreciation. If savings does 
excess depreciation then you will see and increase in capital stock to 
the point where again savings is equal to depreciation. So in the short 
run you want the level of savings equal to the level of depreciation to 
be able to maximize overall well-being. Now sooner or later the economy 
reaches a point where as Solow says where you have a steady state in 
which capital and output become constant. To be able to change this 
steady state you need to change society's ability to produce this can 
only come about through technologcial change. Now technological change 
can take on different forms and the most important seems to be the 
efficiency or education and training of labor. Now this efficiency of 
labor according to endogenous growth theory is a *by-product* of capital 
stock. That is, if you bring a watermelon picker machine into the the 
agricultural fields then workers need to learn how to use and run the 
machine which increases labor efficiency which increases growth  
tremendously, so we have change in the growth rate because of an 
endogenous change. So my point is that it's not just saving that 
affects economic growth. In fact, for the long run what will have 
the most effect for third world countries will be their populations 
on capital-labor ratios and technological change, particularly I argue, 
education and job training.  
2) I'll come back to this later. To understand Keynes you need to look 
at investment, uncertainty and money. This whole thing about talking 
of increasing consumption to increase demand, etc. This is not the Keynes 
of the General Theory. Keynes spent very little time talking about  
the consumption. The name of the game for him was with the investment 
function and the issues of uncertainty for the entrepreneurs and the 
role of money which leads to issues of credit and debt that made 
the economic world go around. Unfortunately when people think of 
Keynes they think of the Keynes they learned in the intermediate 
macro books. Like Ackerly where you have all this talk about 
the consumption and mpc, etc. The consequence if you interpret Keynes 
in this light then Keynes simply becomes a mediocre classical 
economists. TO UNDERSTAND KEYNES YOU NEED TO FORGET SAY'S LAW AND 
THINK ABOUT INVESTMENT, UNCERTAINTY AND MONEY. 
-Ric Holt