Sarah –
Congratulations for making the leap. I think you'll really enjoy the change. I am gradually making the transition to UL myself, but find that all assumptions have to be re-examined.
It has been my experience – and most here have far greater experience than I – that it certainly is advantageous for weight considerations to carry the tarp-style tents. The tents perform admirably. I have several and love them.
You mentioned sharing the tent or carrying two. While space is the primary issue I think there are other advantages to using your own tent, particularly here in the Pacific Northwest. The condensation issue, which affects all tents but more so single-wall shelters, is particularly acute in Western Washington during shoulder season. Cold, driving rains in spring and fall can promote condensation quickly, especially when there isn't a breeze and your tent is in storm configuration. With one person in the tent, I don’t find condensation is that much of an issue – inconvenient, perhaps, but not a huge deal. Add another person and it generally requires vigilance and management, particularly on multi-day trips where the constant wetness is a threat to the downy goodness of your sleeping bag (if you use a synthetic sleep system, you can be more restive).
I can attest that these tents can take a surprising amount of abuse. I've sought shelter in them during driving rainstorms with howling winds and my tarptent withstood it far better than a reasonable person would have expected. I was for the most part dry and happy to be out of the rain.
Of course, by eschewing the big tent you can always use a bit of the space/weight savings to bring a UL camping towel with you to wipe down the walls of your tent.
Have fun! Great pics!
Dirk