Here's a weird way to randomise your playlist. Forgotify is a webapp that finds tracks in Spotify's catalogue which no-one has ever played.
The Forgotify site claims that 4 million songs on Spotify have suffered this ignominious fate, though that number will presumably drop if a lot of people try the app out. In my tests, it offered up a lot of strange material in languages I didn't even recognise and a large number of classical recordings by entirely unknown ensembles. Rock on. It's a free service (you need a Spotify account, but the ad-supported version of that is free too).