Libertarianism and Republican Virtue

I am short on time and effort these days, so I apologize for bringing up my school readings on the blog. I have moved on from Locke’s Two Treatises to Montesquieu’s Spirit of the Laws.  This passage in particular has stood out to me so far:

When Sulla wanted to return liberty to Rome, it could no longer be accepted; Rome had but a weak remnant of virtue, and as it had ever less, instead of reawakening after Caesar, Tiberius […] Nero, and Domitian, it became ever more enslaved; all the blows were struck against tyrants, none against tyranny (pg. 22).

The decay of the American republic has been a worry of learned men since the agreement first took place.  My big question here is not so much about decay or liberty, but rather what virtue is.  I have some conception of it, but any sort of clarification would be great.

Montesquieu treats the desires and defenses of manufacturing, commerce, wealth, finance and luxury as the end of virtue and the beginnings of ambition, which leads to despotism and tyranny.

Given that most libertarians are also republicans (small “r”), how do we go about explaining that the freedom to pursue material goods is what is actually compatible with democratic government?  Was Montesquieu attacking a straw man?