Short tip on how to get this to work:
Create a script /path/to/spotify_open.sh with the following in it:
#!/bin/bash wine "$HOME/.wine/drive_c/Program Files/Spotify/spotify.exe" /uri "$1"
Create $HOME/.kde4/share/kde4/services/spotify.protocol with the following in it:
[Protocol] exec=/path/to/spotify_open.sh "%u" protocol=spotify input=none output=none helper=true listing=false reading=false writing=false makedir=false deleting=false
That’s it, spotify:blah style URLs will now open in Spotify launched through Wine. Chrome just uses xdg-open for launching external apps.