Just to understand better - are you building a game/app? or are you building a business with recurring revenues (like say SaaS)? The answer varies based on this.
Also, are you looking at the data specifically for users you are getting from just this campaign or just your overall revenue analysis?
Sorry I'm asking more questions, but the answer depends on these questions.
You should be careful to map the spend to its own results to judge if its ok to keep spending in the manner. Only that can tell you if its worth spending unless there are other benefits to the advertising spend (higher rankings on appstore for a game for instance)