Andorra is a modern co-principality governed by "Princes" -- the President of France, and the Bishop of Urgell, Spain (Catholic). The ancient and the modern homes and other architecture juxtaposed with the ancient churches, show it can work -- at least on a small scale, and where all seem to agree on the sytem. The modern houses seem to set apart the status of the well-to-do, but how to determine incomes from architecture? Can't be done; Still, there are financial benefits of living and working in and for a tax haven, good employment for the financial wizards ducking and weaving through the undergrowth that traps the rest of us. Andorra modern homes house those who whiz by the rules? Corporate presence: Drive in the town, and see lots of major corporation signs, like Hertz, in little windows of little buildings all closed up (was it a holiday? don't think so), keeping their presence if not much activity alive.
Residential neighborhoods are a mix of traditional and some (far less) modern, and snake up the cliffsides, hairpinning with the main development far below, in the valleys.
This area was part of the "March" estates, where Charlemagne needed buffers against the Moors invading from Spain. Those who provided that service were rewarded with charters, verifying their independent status, a privilege for ownership of land. As a mere privilege, not a right, could it be withdrawn? Most charters listed the rights that were granted, but it is not clear if those also were still a privilege that the overlord could withdraw?
Apparently the uneasy but workable arrangement in Andorra, a power-sharing between the secular and the theological rulers with (it looks like) alternating annual rights of last say, kept going long enough that it was not challenged, either nearer its early times to now. See History of Andorra at http://www.historyofnations.net/europe/andorra.html. The after-you-Alphonse of the Count of Foix, the French, and the Bishop of Seu d'Urgell, the Spanish, morphed into a system of elections now, with a Constitution passed in 1993.