Does usage of acoustic or non-electronic instruments exclude a song from the synthpop genre?
By no means. Many classic acts have used acoustic or other non-electronic instruments to supplement the electronics in their music (an example that comes to mind is Peter Hook’s trademark bass guitar licks in much of New Order’s electronic music, or the usage of a piano in some of Red Flag’s music). While there are purists who prefer their synthpop to be completely electronic, non-electronic instruments do not necessarily diqualify the song from the genre, so long as the electronic instruments are PREDOMINANT in he song. Sometimes a guitar riff or a piano or orchestral accompaniment can add a bit of variety to the music.