I think this letter describes
Not many know of me, and even less have touched what is mine.
Nauru is the least visited country in the world with less than 200 tourist visits in 2011.
A lonely fella I am, like being the smallest pebble in the puddle,
Nauru is a remote island in the South Pacific - it is the world's smallest island (pebble/rock) nation.
Unless you ask the bishop, he owns the title, according to a beaver's idea
Bishop Rock of the Isles of Scilly is the smallest island with a structure. This is from the Guinness World Records, which started as Hugh Beaver's idea. Thanks OP for this!
Reached I am by twelve shiny points, across that much and two more...
On its flag, Nauru is symbolized by a 12-pointed star, each point representing one of the 12 indigenous tribes on the island.
That much and two more = 12 + 2 = 14 refers to the fourteen districts the island is divided into.
Almost exposed myself by now, but before you find me, you should know,
Note the acrostic down the left side the first four lines begin: NAUR
That robbing me of my salty gold, is viable no more for some time now.
The salty gold is the Phosphate (chemically a salt) deposits originating from sea bird droppings.
Nauru had the highest per-capita income of any sovereign state in the world during the late 1960s and early 1970s. The primary phosphate reserves were exhausted, crashing the local economy in the process.
And as a goodbye, I thank you for this conversation, and may God's will be above all!
Nauru's official motto is "God's will first"
P.S. You may want to rob the the Devil instead, just break the king's seal.
The Devil refers to Morocco. Its flag is red and it has a five pointed star, which refers to the pentagram. Red color and pentagram associate to the devil. Morocco has the world's biggest phosphate reserve in the world, and is second in its production (behind China). If you were planning a phosphate heist, this is the place to rob instead. The king's seal refers to the five-pointed star actually representing the Seal of Solomon (King Solomon). Thank you, Vepir, for this!