Ian, wear what you'd like. As the past recipient of several marathon "50-break falls in a row" sessions, or sitting in seiza for an hour with heavy (suburito) in chuden-no-kamae, or mountain running with bokken, by the end of it, I didn't really care what I wore. Come to think of it, spandex booties might have given me more lift by No. 50.
As to cross training, it very well could be outdated material. Interesting point, though, because they tested with electro-conductivity, Max VO2 consumption levels, etc., fairly rigorous, concluding that not so much muscle "groups," but individual fibres their inherent characteristics (e.g., slow twitch/fast twitch percentages in a given athlete) and their trained characteristics (responsiveness to various aerobic/anaerobic/resistance stressors) matter when discussing an athlete's conditioning regimen.