Edward Gibbon's Smithian Defense of Luxury

I wrote a post some time ago contrasting Adam Smith and Jean Jacques Rousseau on the utility of luxury consumption. Smith famously argues that the purchasing of vain trinkets is a crucial means by which the feudal aristocracy sacrifices the basis of its political power. The libido dominandi was once expressed through hierarchical mastery. The miracle of a commercial society is that this same drive can now be satisfied through conspicuous consumption. Here is the famous passage from book three of the Wealth of Nations:

For a pair of diamond buckles perhaps, or for something as frivolous and useless, they exchanged the maintenance, or what is the same thing, the price of the maintenance of a thousand men for a year, and with it the whole weight and authority which it could give them. ... for the gratification of the most childish, the meanest and the most sordid of all vanities, they gradually bartered their whole power and authority.

In the Theory of Moral Sentiments, Smith famously celebrates this process of sublimation as a means of establishing a more equitable distribution of material subsistence: 

[The rich] are led by an invisible hand to make nearly the same distribution of the necessaries of life, which would have been made, had the earth been divided into equal portions among all its inhabitants, and thus without intending it, without knowing it, advance the interest of the society, and afford means to the multiplication of the species.

So Smith makes two arguments here in favor of luxury consumption: (1) Politically, by purchasing ever-more expensive frivolities, the feudal aristocracy sacrifices the material basis of its authority; (2) Economically, by pursuing luxury, the feudal aristocracy produces a de facto redistribution of wealth. (I've written a couple academic articles reconstructing this Smithian reasoning at greater length).

As I point out in that older post, Rousseau offers a similar descriptive analysis, though he curiously praises the older expression of vanity--political mastery and war--as more noble than vain, luxury consumption.

At any event, Edward Gibbon comments on the same phenomenon in a brief aside in Volume I of The Decline and Fall of the Roman Empire (published, incidentally, in 1776, the same year as The Wealth of Nations). He rebukes moralist critics of luxury and celebrates commerce for one of Smith's reasons:

Under the Roman empire, the labour of a industrious and ingenious people was variously but incessantly employed, in the service of the rich. In their dress, their table, their houses, their furniture, the favourites of fortune united every refinement of conveniency, of elegance, and of splendour; whatever could sooth their pride, or gratify their sensuality. Such refinements, under the odious name of luxury, have been severely arraigned by the moralists of every age; and it might perhaps be more conducive to the virtue, as well as happiness, of mankind, if all possessed the necessaries and none the superfluities, of life. But in the present imperfect condition of society, luxury, though it may proceed from vice or folly, seems to be the only means that can correct the unequal distribution of property. The diligent mechanic, and the skilful artist, who have obtained no share in the division of the earth, receive a voluntary tax from the possessors of land; and the latter are prompted, by a sense of interest, to improve those estates, with whose produce they may purchase additional pleasures.

So Gibbon and Smith agree on the trickle-down type benefits of luxury consumption, but we don't find in Gibbon the same political analysis of the collapse of traditional landed political authority.