My dream wish is if someone could make a Pandora-like app ( both of in terms of functionality and quality) built on top of Spotify. I know spotify offers some API but don't know if this would be possible.

IIRC Pandora has a catalog size of about 1 million vs ~20 million for Spotify and yet they have been able to do a superb job in song recommendations. I find Spotify radio to be pretty terrible at this.