(Havard, I think you used a celtic model for the vales, right?)
Correct. I could be forgetting some things here, but I believe the original idea was Vales=Wales. That is, a Welsh inspired culture living in the Vales. I extended that to include inspiration for various Celtic nations though, not exclusively the Welsh. Names like Starmorgan and Vale of Glenfinian in western Ten probably also contributed to this way of thinking.
The second point of inspiration were the maps indicating the presence of Picts in the western parts of Blackmoor. I assumed that these would be ancestors of the Valemen (people of the Vales) and that they were more widespread around Blackmoor in historical times, but that they had been driven Westward by the expansion of the Thonians.
This also helped me integrate some of the lore about Druids that seemingly had no proper place in Blackmoor lore. The existence of Druids would suggest an older culture coexisting with the dominant one. IMC the First Druid, Halgred Forestwalker, who appears in the BMPG (D20) was the founder of the Valeman culture. The Vales Campaign
goes into more detail on this.
Valemen can also be found within Thonia as will be revealed in future installments of my Thonian Provinces Sourcebooks.
There is alot more I could add, but I dont want to risk spoiling future developments in the campaign