Re: That it works, don't make it good.
On kata in aikido....There are different perspectives. Ueshiba is pretty well known to dislike kata, as Mrs. Skoss pointed out. But the fact remains that Gozo Shioda, Tomiki, and other prewar students refered to quite a bit of aikido as 'kata practice'. The mainline of Daito ryu also refers to much of its practice as 'kata practice'. Since the empty hand techniques in Aikido come directly from Daito ryu this has to bear some weight. The early works of Ueshiba (Budo and Budo Renshu) also seem to present kata form. The kata displayed there can be directly traced to the Yoshinkan, Iwama and Shirata Sensei forms you see today.
Interestingly enough, when I spoke with Stevens Sensei about this, his perspective was that in fact aikido techniques as practiced in the dojo were NOT kata, but something different. His idea of kata is influenced by his exposure to more classical arts, where kata (in his perception anyway) are more 'strict' in the movement and response of shite and uke. You don't change the angles, distance, etc. for the situation...you do your best to present the kata exactly as it was taught (again, this seemed to be his opinion). Perhaps Ellis or others more familiar with classical training can weigh in here on this point. Karl Friday's 'Legacy of the Sword' has some interesting points about kata in japanese martial art as well. I also seem to remember the descriptions of how S. Takeda Sensei demonstrated technique as not being as static as you might think of classical kata (a point perhaps on whether or not Daito ryu is koryu, reconstructed or otherwise).
I personally think Ueshiba was focused on 'Takemusu Aiki', or the phase of martial art which is beyond the training methodology of kata. Most of us would like to get to that stage...but I know I'm far from it, and 99% of the time, I am practicing kata (loose definition of kata). Hopefully as time goes by, less of the kata, more of the Takemusu. I think there are good arguements on both sides of this discussion.
On jo waza/kata being an add-on to aikido, as opposed to ken or tachi waza...I'm not sure. The history of the jo techniques does seem fuzzier than the ken or tachi waza (Meik Skoss has some good points on this on fa.iaido). Aiki-taiso and Taisbaki as kata...well, typically, kata refers to two man sets of waza in japanese martial art (as opposed to Okinawan). I don't know that I'd refer to them as kata at all. But they do indeed have a high place in keiko.