In many scenarios (viewing a lot of images, slight editing in Aperture or Lightroom), disk speed can be the limiting factor rather than processing speed. In those scenarios, the faster SSD can more than make up for the lesser processor speed compared to the MBP.
Good point. I'll only be doing minor edits on a large number of photos, and since I cull images in Photo Mechanic instead of LR, that shouldn't be an issue.

You might want to consider a MBP instead of the MBA if that allows you to leave the external disks at home.
Although I love lightening the load of what I take with me, but the security of having the images backed up makes it worth it. I'll most likely take 2 Lacie rugged drives and clone them each night.

Thanks for you advice!