First off I would talk to your LBS...if you are buying 2 bikes you will have more price barganing power...maybe you can get one Satellite and one Quest. Then of course the question is will this be ok with your wife. Is she seriously going to be getting into cycling or is it that she is willing to try it. I used that in the past as a reason to get a lower level bike for my wife...and honestly it was both the truth and a good idea. In the end she did like riding and the bike we got was enough bike at the time. In the end we both prefer road riding though (those bikes were both MTBs and we have neither of them now), so now she has a nicer road bike.

On to the question about the upgradeability. If 2 Satellites is what you can afford, and the bike fits both of you properly (this is key) then buy them. If you like the bike enough upgradign to 105 is not a bad plan...I wouldn't stick DA on it but 105 isn't a waste of money IMO.