When it comes to Saiko's speech, I remember it being said once that she talks old fashioned. Is it a consistent speech-type thing, or is it more of a deliberate sprinkling of words for flavor?
No, she’s not old-fashioned! She’s actually talking in otaku-ben, an (unofficial) “otaku dialect”. From time to time she’ll talk in different dialects like Kansai dialect or Nagoya dialect, and sometimes she’ll throw in old-fashioned phrases, but all of it together just sounds like someone has watched a bit too much anime and now just imitates different characters’ way of talking.
It sort of sounds cute and it’s too bad English translation doesn’t pick up on her speech patterns - although in many cases it would be hard to find an appropriate translation for a certain accent.