Hi, thanks for your response.
The reason I wanted to try switching to Notes.app was that I wanted to hopefully simplify things, keeping all notes in one place Up until now I've kept shared notes in Google Docs, and notes that require images or more formatting than markdown allows in Evernote. But I dislike Evernote for many reasons, and don't want three places where information is kept.
I checked out other 3rd party notes apps and found the all lacking for different reasons. Apple Notes has its limitations and frustrations too, and may not be the final solution, but I do like having a simple app that's integrated with Mac & iOS, that most everyone I know also has.
Anyway I did find a work-around solution for how to get text files into Notes:
1. Run this script on a folder containing text files - it imports them all into Evernote, preserving dates & titles (!)
2. Export from Evernote
3. Import to Notes.app
PS - I have high hopes for BitWriter, the upcoming notes app from nvALT creator
Brett Terpstra. But there's no release date for this.