The most important thing is the content you offer, not the platform it’s available on. All of the social and music sites do the same thing. If you focus on excellent production quality and excellent songwriting (as much as the R.F market will allow of course, simplicity sells better then complexity here I believe) followers and fans will find you wherever you are.
When I myself was having little success advertising, instead of searching for the “golden egg” of advertising, I took a step back and looked at the musical content I was promoting. I changed some of the content and got more picky about what pieces I used to draw people in and – boom – referrals started pouring in.
So Moccc, I don’t think the questions is whether Soundcloud effects sales or not, the REAL questions is, are you using the right bait to catch the fish you’re after? Customers in a sense (sorry buyers for the crude analogy!) are like fish. There are many different types of fish and they all have different kinds of bait they are attracted to. As authors we must establish 1.) Who is my target audience and 2.) Am I using the correct bait to attract my target audience?
A shark is attracted by blood, a rubber or plastic worm doesn’t do anything for him. Hope I make sense 