I have been checking peoples Spotify settings whenever I get access to there computers for service and stuff like that. And almost all people don't get all they can from Spotify. Most of the computers I checked uses the premium version, the free version isn't much fun anymore with all the limitations. If you have a premium account most songs are available in 320kbs but the standard setting is only 160kbs.
In the menu Edit -> Preferences... this can be corrected! Check "High quality streaming" and uncheck "Set the same volume level for all tracks" to get the full range of the track.
On your smartphone you go to the Settings (the small gears icon in the lower right hand corner). Set both Stream and Sync to High Quality and if you ever have bad reception, or anything else that gives you lower data transfer speed, just change the stream setting temporarily. I usually sync all my tracks because Sppotify uses a lot of battery power when streaming all the time!