Seems like I have incense, a plantation, and road -- but no incense listed as a resource in Yonna... nor in the further off city I want it in.

Nearby corn hooked up fine.
http://www.bemont.net/inc.jpg
So what am I missing here?

You need Philosophy as well to get the resource

Several resources in FfH can be hooked up for the plot bonus before you can actually use the resource.

Specifically, you can build plantations on incense at Calendars, but you need Philosophy to get the resource. Mining reveals copper, but you need Bronze Working for it, and iron is revealed by Smelting but needs Iron Working for the resource benefits.

Reagents are like Incense too - need KotE for the resource but Calendar for the improvement.