I would NOT top up CPF for the illiquidity reasons you mentioned.
4% is nothing if you cannot use the CPF money for your private uses.
The 2nd reason is also very valid, if you can get higher returns than 4%, why do a non-reversable transfer to CPF? The only thing you need to focus on is that the higher returns is only valid for long term, so be prepared for short term swings that may be unpleasant compared to the "stability of 4% yearly".
I would NOT top up CPF for the illiquidity reasons you mentioned.
4% is nothing if you cannot use the CPF money for your private uses.
The 2nd reason is also very valid, if you can get higher returns than 4%, why do a non-reversable transfer to CPF? The only thing you need to focus on is that the higher returns is only valid for long term, so be prepared for short term swings that may be unpleasant compared to the "stability of 4% yearly".