1. I think the practically of training weapons lacking a tsuba has more to do with production than fashion. You can purchase tsuba for bokken for additional cost. I also know of several competent craftsmen who have fashioned their own tsuba. There is a measure of safety the tsuba offers as well as the reflection of sword techniques that become more difficult when you have to compete with a tsuba (wrist cutting, for example).
2. Weapons should should always be treated as serious and potentially dangerous. The proper use and awareness of what your weapon is doing is essential to weapons work. To make weapons work a frivolity is simply incomprehensible. If the bokken is representative of a sword, then you are using a dangerous weapon. If the bokken is nothing more than a stick, then you are not practicing sword work. Grab a shinken anywhere you want to, by all means.
I have not purchased a tsuba yet, only because I believe the best ones are custom fit to the sword. Kingfisher woodworks sells a great bokken/tsuba combo. I am not sure if "tradition" plays a relevant role in your decision to use a tsuba. Every day we see non-traditional hakama, gi, tabi, etc.; if we let Mossy Oak hakama in the dojo, are we really arguing about a tsuba?
(nothing personal, as long as the camo doesn't smell like deer p*$$...