I have a Samsung Galaxy S3. Like a lot of other people I had the file local file syncing issue. I could "download" files from Spotify's servers that weren't local files, but I couldn't get it to copy files from my computer to my device. I tried everything listed in every thread I could find. Spotify just wouldn't find my device at all.
Here's what finally solved the issue for me.
1.) I disabled the firewall in windows completely, just to rule that out. Didn't seem to have much of an effect by itself. Keep in mind I've previously allowed those ports for Spotify and this is not ideal but I was desperate.
2.) Downloaded an app called DroidWall from google play.
3.) Under White List, I checked "Any Application". Not spotify by itself, but Any Application, both for WiFi and cellular networks. I imagine it would work with just WiFi checked, but in the interest of being thorough... I also believe it will work if you check just Spotify, but might want to try Any Application just to see if it works first.
4.) I applied the settings by hitting the back button in Droid Wall.
#success
5.) The weird thing is, even if I disable the firewall in Droid Wall afterward, it seems to still work, at least temporarily. I think it just sends some packet or something that wakes things up. Could be that once it establishes a connection you're good to go. I just re-enabled the windows firewall too, so man...I've got no idea what the hell is going on here. If the app is working fine and I re-enable the windows firewall it's fine. Then I restart the app, it can't find my device. As soon as I re-disable it, it shows up within seconds.
6.) As a worst case scenario, if any/all of the combinations above don't work, I can go into Droid Wall and toggle the "Any Application" white list and it will show up. Obnoxious to have to do that, but it seems to work.
It's an incredibly fickle beast, but I've been able to get it work somewhat consistently all evening after struggling with this for like a week.
This was (is?) incredibly frustrating and I'm just sharing this in the hopes that it will help someone. If I uncheck All Applications in Droid Wall or I re-enable my Windows Firewall, Spotify can't find my device anymore.
For the record, I believe Droid Wall requires root, which would make sense.
Hope this helps someone.