Facetious or not, that is precisely what immigration is, no? Loosening immigration policy is something that the deflating and aging Japan has considered.
As far as spending and investing, I think it concerns the most efficient use of capital.
An investor can make bad investments and make value simply disappear, because valuations get increasingly more speculative the more risk is involved.
A common spender, however, is likely spending on highly competitive retail products whose fair market value has trimmed mostly all of the risk.
So, I'd say spending and investing are equal in idea, yes, but when you spend on a razor or a box of cereal, it is a very efficient transfer of utility and labor. You're not likely to spend double on something you know isn't worth that much. The amount of utility you get from a a razor is more than the cash you spend, and so it's a positive sum game for you and the producer. Investing, however, is not that clear, and can be wasteful, so it behooves a society to spend its capital as efficiently as possible. It just comes down to the risk involved. Risk management, always there...