Files imported before using the defaults write command were imported as text, rather than as generic files to be displayed using QuickLook. To change the type of an existing record you would need to rebuild the library. Alternatively, instead of using the NonTextExtensions setting, you could use:
defaults delete com.c-command.EagleFiler NonTextExtensions
defaults write com.c-command.EagleFiler TextFileTypesForQuickLook -array md ics graffle
This will make the files import as text but display using QuickLook, so it will also work for previously imported files. This is probably a more future-proof choice, too, based on how I’m likely to integrate Markdown support.