Too simplistic a conclusion. There is no evidence that political parties do not do songs. In any case, the SDP is rather much a mirror of a political club and votes do not matter to it. Not that it is a bad thing - it could be the best niche market it can carve.
The last from a rumour-mill goes that the SDP plans to tweak its image from a "law-challenging, suit-garnering, protest-oriented" one in 2009. After reading the first few entries, I somehow surmise that the new direction would take the form and be akin a "hip / trendy / relaxed / fun / creative" political gathering. Perhaps that would be more sustainable.