Sharon,
Flat picking a 12 string isn't that difficult once you get used to the feel of the instrument, provided that the action is low enough for decent playability.
Dunkle,
You won't have any problem with playability on a Guild 12 string. The double truss rod system on all Guild 12s keeps the neck in great shape.
What does it for me playing a 12 string is tunes where you can hold a chord shape and keep a lot of the strings ringing at once while playing ornamental figures or solos.
--Finn