I have 2 folders one called "Ambient" and one called "Dance", sometime I add new songs to these folders and then I do
File -> Add Folder to Library
Is there a way to have 2 playlists, based on the songs' directory ?
Smart playlists use the META data that is stored within the audio files themselves to make selections based on your criteria. Example of META data include the song title, length, rating, and so on. The folder that the audio file is stored in is not considered meta data, and is not referenced at any point within the audio file itself - this is managed by the iTunes library XML file instead. So you cannot do exactly what you are doing, but you might be able to acheive it by changing your methods.
Instead of splitting your tracks by genre into seperate folders and then importing them, change your methods to tag the files with the appropriate META data after importing to select a suitable genre. After importing tracks, no matter where they are located (and as an aside I would always reccommend using both allowing iTunes to manage your media, as well as copying into your library rather than just referencing them to their existing locations) just select them all, right click and select get info, and them change the genre to either Dance, or Ambience etc. Then create a smart playlist that searches for audio files that match the Dance or Ambient genre META data.