"Over-investment" and "under-consumption" wording assume that there is some "proper" level of consumption and investment. But there isn't. If milk becomes money, their utility will grow. If, say british scientists would discover that milk, added to petrol, would double mileage per gallon, milk consumption will grow, along with investment into milk production. But we won't call it over-production and over-consumption. If milk, apart from drinking, can be used for something else, it's utility will grow and it is normal, rather than "over".
You're right of course, but I meant with "over-investment" and "under-consumption" as compared to the hypothetical market situation that would exist if the commodity were just produced and consumed for its consumption and eventual capital utility, but not for its speculative aspects.
The difference between milk-that-is-discovered-to-enhance-petrol and milk-that-became-money is that the first is a new consumption aspect of milk, while the second is a speculative aspect of milk.
The demand for an asset (which can be a commodity) has normally three origins:
1) consumption
2) capital (that is, it is a means of production)
3) speculation on later demand
I was setting 3) apart and my "over" was with respect to the absence of 3)