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.