So it looks like the main benefit of the Dutch is going to be the Polder. The video released today had it at 412 in late Renaissance or early Industrial. That's equivalent to a resource tile (Wheat would be 51 for example). Besides that they are still a Marsh, so if you have a few adjacent you get a mini Great Wall in the bargain.
Edit: And that's on a Marsh. On a Floodplain it would be 513
Edit 2: snipperrabbitt!! points out in the main thread about the video that it looks as if Polders create trade routes without roads as well.
Edit: And that's on a Marsh. On a Floodplain it would be 513
Edit 2: snipperrabbitt!! points out in the main thread about the video that it looks as if Polders create trade routes without roads as well.