Hey SumSmug...welcome to the forums and good luck in your search for the perfect Airstream for your needs. You're in the right place to get the answers and do your research....and get personal input from folks who have been there.
I'm only 5'8" so I can't help you with the height thing.
I'm fine in the AS, though but I think most have to duck just little going in and out the door...it becomes 2nd nature, though.
30' and under is a good length for 2 people...heck, ours is only 19' and we are fine, of course we are not living in it, which makes a difference. You can find a layout with a permanent bed in that length and you are right, having to bring down the bed every night can get old real fast.
And you should even be able to find a model with a desk...I know that's possible with newer AS layouts...not so sure about older ones...but certainly you can have a dinette at the very least...
I wouldn't automatically rule out a newer unit if I were you..you can find some good buys out there, and if you perisist, you can find a well-treated lateer model AS...less to redo, less refurbishing money, and may have ammenities you will enjoy...unless, that is, you want an older or vintage rig.
But I do know the perfect AS will find you! Part of the fun is the hunt...good luck with it!