At what income bracket does it become worth topping up SA / SRS, to enjoy tax savings? I'm 26, earning $28,000 and paying tax of $160 a year – not sure if that's worth?

My opinion...

If you have spare cash for investment, i would say to try to grab the lower hanging fruits first. Plan for CPF-SA top up first till you reach a combined amount of $60,000 (inclusive of OA, MA, SA) to take advantage of the extra 1% interest (5% for SA, 3.5% for OA). This will likely form the bond component for your retirement.

Once this is in place, consider putting to SRS where you have more flexibility to invest in SGX stocks, withdrawal (with a penalty of 5% before statutory retirement age of 62 currently, or first $400k (since 50% will be tax deductible) no penalty after withdrawal for a period of 10 years. Of course, you will need to learn more about investing.

The tax-relief will start to make a difference only once your assessable income is above $80,000 (where the tax rate is at 11.5%). Meaning to say, every $1000 put into SRS/RSTU will reduce your tax payable by $115.00

At 7% (between $40,000 to $80,000), it is debatable because every $1,000 you put in will reduce your tax payable by $70.00.

Your tax bracket is 2%, so your effective tax savings is only 2% of what u topped up. But topping up the SA is still a good retirement planning savings. As it offers 4% guaranteed return. additional 1% if u hv less than $60k combined balance.