A wireframe is something I always pump out of Cinema to help layout timing, framing, etc. I was looking for the same with Terragen, and I ended up settling on setting the quality to .2-.3, no GI, and super low quality clouds, rendered at 960x540, and even a smaller one I think. I got the whole 250 frame animation out in a couple hours; which wasn't too bad as I was able to set it up on another computer and continue working on mine. I found it really nice to have something more than the wireframe because I could see how the shadows and textures were playing, and I could get much more done the next time around.
Once I had the basic camera move set in Terragen, I exported the camera and landscapes to Cinema via FBX and microexporter to do the camera tweaks (Terragen's keys are impossible to work with!) and pumped out wireframes from there to make really nitpicky changes.
So, yes, I'd second having the wireframe straight from Terragen, but lowering your settings is still pretty doable (I suggest making two render nodes-one with your final quality and another for your quick renders).