I wouldn't say that Touhou has slowly become less and less traditional over time, as the entire project always had some western themes about it also (So it isn't all Touhou!). I mean yeah, youkai and so on are really common in Touhou but this is also the same series that has a European based mansion which is run by a European based vampire. I'd say what mostly differs one generation of the project from the other one is how it's been portrayed.
Like EoSD to StB had rather simple backgrounds with rather simple colours (unless you count spellcards and character designs), where as with MoF to HM have a lot more backgrounds with a lot more stuff happening in them. Why did I not mention DDC? Because those games are going to be part of a new generation which right now seems to be a mesh of old and new.
So yeah there's my little take on it. Wish I could think of another word that isn't generation, but the wiki has it listed like that.