The original copies of all my digital media lives on a 27" i7 iMac, and that is where I do the vast majority of the type of work that you mention.
Mostly... it is because of the 2TB diskspace, large monitor, and of course processor.
However, on the MBA I can do any of my workflow with the possible exception of video transcoding (I never tried).
I use Aperture 3 and the MBA handles it with ease. My photo library is larger than yours. My main aperture library is on the iMac, but I can easily export libraries and consolidate masters to do photo work in the field. I have no desire to have my full library on my laptop.
I have a quite large and very complex excel spreadsheet with dozens of tabs and huge complex pages with thousands of variables and extensive conditional formatting which the MBA handles with ease. There is no noticeable difference between it and the i7. I am in that spreadsheet many times every day, and it is one of the most complex I've ever seen.
Irrespective of what laptop I own... I will have a heavy duty desktop for many reasons. Given this... it just intensifies my resolve to have as comfortable laptop as humanly possible. I have pretty much completely stopped using my 15" MBP because the MBA is 10X the machine in terms of ease of use. My wife also has a 15" MBP... and she keeps asking me when I am going to buy a new MBA for myself so that she can inherit this one.
As far as I can tell... the MBA form fact is about as perfect as I can imagine in a laptop. I would like it to be a bit lighter, and I would like it to have 4GB of RAM. The battery life is just fine. If they made it an ounce heavier to give us a longer battery I would be disappointed.
I have owned about 20 laptops in my life, most of which were performance machines. In my opinion, the MBA is the very best by far, with nothing in 2nd place.
Having said that, I would not necessarily recommend if it was going to be a sole machine. Luckily, I do not have that handicap.
/Jim