Can't help with the first question, as I don't really know, but I have a bit of my own insight into the second.
I feel that aiki taiso are a kind of kata, so to speak. We go through a motion alone, such as the karateka does, and, as many a karateka has complained about, we feel that these 'mini-kata' have no point, no combat value, and therefore no meaning. However, when applied as bunkai (or in our case, waza), we can see that they are indeed useful in not only ashi-sabaki but also the hand motions, hip movements, etc.
Like the kata, I believe that they are a good thing. Everyone has to start somewhere, and where better to start than the beginning?