The original reason why I provided responses in the Spirituality section that resulted in a post being split off to start this thread was to help foster this notion (feel free to substitute in "Training in the gendai budo descended from Daito-ryu" for "Aikido", as there are many of us in aikido's cousin arts who feel the same way):
Aikido is self development.
Before this thread goes into a death-spiral of rhetoric like so many pertaining to internal training before it, I'd like to say/restate that, as students of aiki, it makes sense to follow the fine examples set by Ueshiba and Tohei and explore methods outside of the confines of our respective budo silos to foster self-development within our martial training.
Many of today's aikido students embrace the notion that Japanese yoga, which completely lies outside of Aikido's martial arts ancestry and martial arts as a whole, led Tohei to key insights related to his esteemed skills and teaching methodology within aikido. Ueshiba sought inspiration and clarification of his purpose as an aikidoka via a Japanese religion and the Chinese philosophies applicable to internal martial arts. Ryuho Okuyama, who founded Hakkoryu, combined his Daito-ryu training with knowledge from Japanese and Chinese traditional medicine, and derived the conclusion that it is important for students "to relax both mind and body so that one$B!G(Bs Tanden or Hara (center of gravity) settles in the proper place" (as quoted from Hakkoryu's public website). Did this come from Daito-ryu, traditional Asian medicine, or both? Regardless, aikidoka who've sampled or cross-trained in Hakkoryu have pointed out that this statement sounds a lot like "weight underside", yet there's no public record of Okuyama having studied Japanese yoga. However, Ueshiba once said, "If your opponent strikes with fire, counter with water, becoming completely fluid and free-flowing." This could also be considered a tenet of Hakkoryu, and it's quite likely that Ueshiba and Okuyama came across the same sources of this knowledge. However, the statement is not just a general yin-yang tactical metaphor, but rather a reference to discreet aspects of internal training and application of internal power -- though the sources are likely from outside of Daito-ryu.
Ron Ragusa wrote:
Ki exercises, Ki testing and technique are the seeds of Aikido, not the art itself. Once they're planted in the student diligent training and honest self examination are required for them to grow and bear fruit.
This pertains to "IP/IS training" methodologies (as they've been too conveniently carved out as separate from Ueshiba's or Tohei's IP/IS training methodologies) as well. To put it simply, one could say that Dan Harden's methodology, for example, provides specific models for extending ki once weight is underside, and in and yo from the one-point are established by the practitioner. The precedents set by Ueshiba and Tohei clearly spell out that exploration of relevant ideas and practices beyond what may be considered "aikido" at a given point in time are indeed part of what makes aikido unique, progressive and effective as a both a physical and spiritual endeavor. If the Chinese classics and Japanese yoga are part of this precedent, then it is quite reasonable, if not logical, that an IP/IS training methodology derived from Daito-ryu and vetted by men who've personally trained with Ueshiba and/or Tohei, is worth any aikidoka's time to investigate, if not pursue for the sake of self-development -- or at the very least, not to be dismissed simply because it is not part of one's silo of choice. After all, "ai" doesn't mean or connote avoidance or dismissiveness.