You can totally go for the 1.6 MBA. I have a quite similar setup. I use a 1.6 Rev. A MBA at work and an 24" iMac at home.
At work, I use all kinds of office apps, specially Keynote '09, doing lots of heavy presentations with there, with tons of images, charts and videos. I can't use some of the complex animations, but that's something that even my 2.4ghz iMac can't do as well.
I also use OmniGraffle and Coda a lot, and some Photoshop here and there. All of that while running iChat, Yahoo! Messenger, Skype, iTunes, Mail and lots of tabs open on Safari 4.
There are some occasional slowdowns, but those are completely related to playing heavy Flash stuff on Safari. Just close the tab and everything's fine again.
Sometimes I considered switching to a Unibody MB like you're now. But when weigh the pros and the cons, here's what I get:
Pros:
1 - Better graphics (9400m)
This could be achieved with a Rev. B Air
2 - An extra USB port
I don't care, I never use more than 1 usb port at a time, even on my iMac
3 - An ethernet port
This is nice, but I rarely use it. I bought the USB Ethernet adapter, and I don't see an issue to bring it along.
4 - Ability to upgrade to 4GB RAM
This would be an welcome addition, but TBH, I don't use virtualization, so I never top the 2GB on the Air. OS X has awesome memory management.
5 - Ability to upgrade to SSD in a near future
This is by far the killer thing to me. I've played with SSD machines, and I'm completely crazy about it. Since the Rev. A MBA is likely to be impossible to upgrade to SSD, this is something that would make me switch. But only because it seems I won't be able to upgrade my Rev. A MBA with an SSD.
Now, the cons:
1 - Optical drive
Sorry, but I couldn't care less about it. I simply don't use them for at least 3 years or so. And I can't avoid to think about how much space it takes on the laptop that could be used to other things like an additional HDD (Optibay i.e.)
2 - No firewire
Again, USB can be expanded via a USB hub. But since Apple took away the firewire on the MB, it became far less attractive to me.
3 - Added weight and thickness
Know something I love about my MBA? It's thin like my Apple Keyboards. That's something that makes a world of difference once you get used to type on it. Try to type on a regular MB or MBP and you'll miss the added comfort of its thinness. And about the weight, it's a world of difference.
4 - Crappy screen
I LOVE the MBA screen. I can't look to the MB screen anymore without noticing the difference in quality. I used to have no issues with my previous white MB, but now that I got used to the MBA screen, I simply can't go back
So basically, this restricts my upgrade options to a Rev. B MBA or a 15" MBP -- this one may be a lot bigger, thicker and heavier, but it got so many advantages (powerful graphics, bigger screen, firewire, etc) that at least it can compensate the tradeoffs.
Sorry for the long post, but I know exactly how you feel. If you toyed with the Rev. A MBA and liked it, then go for it. At least you'll be paying nearly half of what I paid a year ago.