With some version of the Spotify app the "Import Playlist..." item was suddenly gone. That's why I wrote iTunes2Spotify, have a look here:
I tried to install your app on my old MacBook, and even after installing the Mono framework I receive this message.
"Impossible to open the following disk images
iTunes2Spotify.dmg => no file system mountable"
I'm a bit old fashioned, as I run with :
Mac OS X 10.7.5
I'm very interested by your solution.
Does it work when you have your library on a folder on aNAS hard drive that goes through the WiFi?
I don't know about the "no file system mountable" error, I would think that it might have something to do with your OS X 10.7.5 setup, maybe you're missing some tool there or something. I run OS X High Sierra and Mojave so I can't test this out.
Maybe you'll find some answers here.
Please contact me through itunes2spotify(at)mrupp.ch and I'll send you a link to a ZIP file as an alternative to the DMG file...
Do you do this?Click the Menu icon in the upper left corner of iTunes windown, then click Show Menu Bar, just press Ctrl + B. Then import the file/library/import list.