Pulled this mess together by stealing from other ideas. I take no credit for any of this, just wanted to make this somewhat convuleted fix available. I won't help you set it up, so don't ask me. (You can ask, but I won't help.....)
In a nutshell, it completely clears out the Spotify cache EVERYTIME it launches.
1) Create a shell script on your Mac
#!/bin/bash
#du -sh ~/Library/Caches/com.spotify.client/fsCachedData
#du -sh ~/Library/Caches/com.spotify.client/Browser
#du -sh ~/Library/Caches/com.spotify.client/Data
cd ~/Library/Caches/com.spotify.client/Browser
rm -rf *
cd ~/Library/Caches/com.spotify.client/Data
rm -rf *
cd ~/Library/Caches/com.spotify.client/fsCachedData
rm -rf *
#du -sh ~/Library/Caches/com.spotify.client/fsCachedData
#du -sh ~/Library/Caches/com.spotify.client/Browser
#du -sh ~/Library/Caches/com.spotify.client/Data
open -a /Applications/Spotify.app
2) make it executable (something like chmod +x <filename>). Might need to be root user here, depends on where you put the script, I guess.
3) I used a great utility called "Appify" (google it), and turned the shell script into an app.
4) Copy the Spotify icon onto your new app.
5) Drag it into your dock, remove the actual Spotify app, and voila. The Spotify desktop app now launches and loads content in seconds. You can (gasp!) browse artists, your library, etc, nearly instantly. It will BLOW YOUR MIND.
Caveats - this removes Spotify cache. Not sure what all it's used for (besides the obvious), but I have noticed zero issues. I suppose if you were on a data plan or something you might care. I don't. Also, this script *could* cause major havoc if entered incorrectly and ran. Use at your own risk.
Spotify - for God's sake. Fix this. Keep 100GB of cache on my local drive, I don't care, but make the app USABLE. It's been a mess for months (years?).