Why need to spend $6,667 on CC and $1,000 on RSP? You just need to spend $0.01 on CC and $100 on RSP to unlock these two category.
Assume someone has $6,667 salary, $0.01 CC spending and $100 RSP, POSB Cashback Bonus will give $22.5 cashback per month ($20 from salary, $3 from ETF RSP minus $0.5 charge). This is equivalent to 0.54% p.a. interest rate for 50k (or 0.27% p.a. for 100k). And he's free to top-up the 50k (or 100k) to Singlife, ELASTIQ or other products to get another 1.0%~1.8% p.a. interests. So total interest rate is 1.54%~2.24% p.a for 50k (or 1.27%~2.07% p.a. for 100k). If the interest rate from Multiplier is lower than this, it's worth to convert.