Babylonia: the Neo-Babylonian Empire, at its peak (under king Nabonidus), extended south as far as Medina. Thus, I’d add some higher settler value (3 or 5) to
Tayma and
Medina (known back then as Yathrib), which were the most important centers of the region. Additionally, a slightly higher value for
Dilmun (2) may be added. Besides their economic-political ties with Mesopotamia, they had foreign dynasties associated with the Babylonians (both Akkadian and Kassite kings) and were vassals from the Neo-Assyrian and the Neo-Babylonian empires, according to Mesopotamian inscriptions.
Persia: all the ancient Persian empires controlled parts of Arabia, most notably the Sasanians, who extended their rule over much of Oman, Yemen, and the Persian Gulf. Accordingly,
Mazun and
Hagar/Gerrha served as regional capitals and could be assigned higher settler values (3 or 5). Additionally, the war value for Yemen could be increased to reflect its conquest in the late 6th century CE.
Ethiopia: it is one of the few civs that have higher settler values on Arabia currently, in Aden (10). Historically, the main cities on Aksumite Yemen and in Hymar (a Yemenite kingdom that was ruled by an Ethiopian king shortly before its collapse for Sasanians) were
Sanaa and
Zafar, whose settler values could be increased (5). On the other hand, Aden could be decreased (3) – it is a nice spot and makes a very nice transition for later Yemen, however Aden only became clearly the main port in the region during the British Protectorate (19th century).
Arabia: unsurprisingly, it is the civ with the highest settler values in the region. My only suggestions are to increase the values (5) for
Medina,
Al-Hasa (ancient Hagar/Gerrha), and
Sohar, since those were very important regional centers in the medieval era.
Swahili: mostly as an easter egg, given they could arguably represent the later Omani Empire, with some settler value in
Muscat (3).
Ottomans: surprisingly, at least for me, the Ottomans don’t have almost any settler values in Arabia. So, considering regional capitals or cities that flourished under them, would increase the values for
Mecca (5),
Medina (3),
Hofuf (ancient Al-Hasa),
Hodeida,
Mokha/Mocha and
Sanaa (2).
Portugal: I think the Portuguese have significant war values on the region, but it may be interesting to add some settler value to
Muscat (5), which was one of their main ports on the Indian Ocean.
England: considering the British protectorates in the region, would give some settler value for
Aden and
Muscat (5), as well for the main Trucial States towns,
Abu Dhabi and
Dubai (5).