Aedyr interests me because it seems like a culture where they're willing to explore it's multiracial nature, and the consequences of the differing lifespans, for example.
Though generally I feel that a big problem with making the cultures more interesting than the races is that the main two cultures in the game are pretty uninteresting. Dyrwood is just bland, while the Glanfathans mostly just seem like your surly barbarian types.