SPP is a weak party that revolves entirely around the Chiams, both of whom are old and Chiam See Tong is in poor health. Other than the Chiams, I don't see any strong members in their party. It's like those old HK kungfu shows, where the martial arts school only has one strong fighter, the master of the school, while the rest of them are duds who make up the numbers.
SPP is a weak party and most sinkies have little confidence in them. The people of Bishan-Toa Payoh showed more confidence in a Wong Kan Seng who let Mas Selamat escape under his watch than a weak SPP who clung onto Potong Pasir for decades.
Even if all the sinkies get retrenched and replaced by NRIs, Pinoys and PRCs and end up working as taxi drivers, security guards and hookers, the majority of them will still vote for PAP even if they hate PAP and wish PAP members an early death.