We can argue back and forth about there merits of Spotify but you can't argue with its popularity and its increasing presence in the conscience of the music listeners – casual mainstream or not.
Building your entire marketing plan around Spotify is not smart because you do not control the conversation with your fans. Spotify owns that conversation, they set the price, they charging you for it and can change the rules any time – it is their house. There is a saying when it comes to marketing your stuff on social platforms, “Never build a house on rented land.” This applies to music marketing too.
Use Spotify. Use Facebook. Use YouTube. Use whatever platform you can find fans on. BUT always be looking for a way to get the listener over to your world.
Bottom line, I like to have my music where there are a lot of music fans who are consuming a lot of music and who just might like my kind of music. Then I focus on ways to get them off of there and into my world (i.e. email list).
What's your plan?