Note that I do not actually own either iMac or MP (my first Blackbook is finally in FedEx's grubby paws now!!!)
My vote is for the two 24" iMacs. I am assuming that you are setting up two desks for both you and your wife. I say that because obviously you want your computers to match. Aside from that, I think that the two iMac's are more easily accomodating to a non-modern, classic look (especially if modified with colorware) while the MP screams modern, even the screens. Odd's are you don't need the 30" and that the 24" will be more than enough, unless you plan do serious movie watching (which seems counterproductive especially when you don't even get Blu-Ray yet (built in at least)). Not to mention, the simplicity of iMac's design means that you will have more storage space because you won't have to hide away the MP tower. Plus there is just the general rule that it's not the best idea to hide away any kind of tower into a small wooden hole (heat issues). Not that I expect it would be a problem, but just incase, you might have some bluetooth problems if the signal is going through a lot of wood and metal (others feel free to correct me on that).
As for being able to sync up your iPhone, just keep the cable in the desk. It's only one cable so it can be kept out of sight for visitors. Then whenever you need it, just grab it for the time and then rehide it.
Remember, the last season iMac's were good enough for that movie about the designer from hell...Devil wears Prada. If you're wife needs any more convincing, show her those clips. They comp's looked excellent in that kind of setting. Granted they are no longer white, but I think that their being Aluminum makes them look better, without having the box-y lines of the Mac Displays.
Edit: Plus, I'm surprised that no one has mentioed the convenience of having your speakers hidden. That should definitely be a plus towards the iMac.
Edit 2: Also, the iMac has the built in iSight camera for easy video tele-conferencing or just calling the family.