Topping up CPF, I think it is very individual, cos not all sharing the same agenda
If one know and where to invest, then it is excellent, as still able to achieve the higher return with liquidity.
RA is good as promise 4% compounding but on one condition which is - the fund will be locked forever and cannot be withdrawn at all but only can wait for monthly payout upon reaching the age of 65. So if one is able to accept this condition and no place to deploy out for return and have excess extra fund then i guess can consider to top up. But think first before top up, cos it is one-way, irreversible.