One interesting question: what is "density"? Is it number of people per road-mile? Number of households? Structures? Sales tax revenue? Property tax revenue? Property value per road mile?
LA has somewhat insane property values right now, and by the metric of millions of dollars of residential value per road-mile, I think one might imagine the density to be sufficient to afford decent streets. Of course, that does not translate to municipal budgets or even to disposable income of the owners or the residents in those properties.