There is no such thing as a 'proper distance'. The distance that will work in a given situation depends on many factors - the mere physique of the involved persons being one. Practicing the japanese sword can teach you a lot about how to judge and adjust distance. It can also teach you a lot about irimi - the very first step in which the whole thing is decided.
I think the japanese sword can teach you a lot about the principles of Aikido - and that these principles are relevant and unavoidable if one wants to do any martial art. After all there is never a reason to be in a bad position opposing the opponent. Some issues simply have to be fundamental and mandatory.
Of course this could just be me
