Templated polygon turns into a wireframe
 

I'm following a tutorial at the moment that requires me to work on just one side of a model, and duplicate the other side as an instance. The tutorial then tells me to right click on the new, instanced side and select "Actions > Template". Supposedly, this shouldn't change how the polygon is viewed, but no matter what I've tried I can't get it to appear smooth shaded like everything else.

I'd appreciate it if someone could tell me where I've gone wrong.

well, I'm still fairly new at maya, but if I'm understanding your problem correctly, you need to select the poly half that isn't smooth, and go Edit Polygons>>normals>>Soften/Harden>>option box

Select all soft, and click OK. voila!

Hmm, perhaps I wasn't very clear. The duplicated and templated half isnt shaded at all in any of the perspective views - it just appears as a grey wireframe even when I select 'Smooth/Flat shade all'. It's not really that great a deal as it turns out, I've just continued with the tutorial without templating one side. I'd still like to know how its done though, because it would make things a bit easier.

You could add it to a layer and then make it a reference...