Since サヨウナラ, when written in katakana it gives a more cool/deep nuance. How about ありがとう? Do Japanese people choose to write it in katakana if they want the nuance of the word to look cooler? It's ...
I'm looking at this picture of the 日米和親条約 (Kanagawa convention) from the late Edo period and it seems rather strange: It looks like the non-kanji parts are rather haphazardly written in katakana ...