A Query...

[The Sixth Wizard]

What else ... would keep [Dol Amroth] at such a level of dignity and respect if he did not provide some genuine value to the kingdom of Gondor? A lucrative trade in exotic spices and goods of all kinds seems a likely source of wealth for a coastal city-state such as Dol Amroth.

If there's one thing I know about trade, its that if you can take the cargo by sea, you'll never go overland. Why go to Dol Amroth and unload all the heavy stuff, then cart it miles and miles to Minas Tirith, all the way trying not to get arrested or killed because you are an outlander trader? It would be much easier just to sail merrily up the Anduin, no? Even if what you were doing was illegal, you could smuggle things on ships with ease compared to over land. Dol Amroth would have its fair share of exotic trade, but certainly not as much as Pelargir or Minas Tirith.

The "dignity and respect" comes from the elven character of the city and the high ranking knights there.