Is it an investment? No, and anyone treating gold as an investment is acting very foolishly. Gold is money, plain and simple. It has retained its essential value for centuries.
Gold has real value as, for example, a material used in electronics. That is about it aside from aesthetics.
Additionally, humans ascribe (nonexistent) value to gold for the reasons you mentioned. You can certainly argue, as some others seem to, that being suitable for use as currency is value inherent but that assumes the necessity for currency. In the past, perhaps.
However, even then the unspoken and often ignored requirement is that there is something of real value that the currency can represent. This also ignores fluctuations in the perceived value of gold, which belies its valuation not being tied to its function as currency. Arguing that e.g. mining for gold is a service whose end product is currency, "consumed" by others is circular (but in reality that does not matter.)
I suppose it can simply be said that gold is considered to have value by common agreement; but that agreement is not irrevocable unlike some believe.
Not to detract from your point though - it just has wider uses than merely electronics :-)
EDIT: Also, why is it so hard to imagine taking care of the debt? Or is it because he has little faith in taxpayers' willingness to pay into it?
I imagine that's why Scott's friends are buying gold. Not because they think the end of the world is nigh, but because they think the dollar is going to have to be devalued to sidestep the crushing debts that have been run up.