For tax rebate sake: 1. Is it wise to RSTU 8k each year for my spouse CPF which near 0 balance in SA from now at the age of 40 till 55? 2. Priority should be SRS first or spouse CPF?
Assume your spouse is not working, i.e. annual salary less than $4k, you get $8k tax relief each year by RSTU $8k to your spouse SA each year. The actual tax dollar savings depend on your tax bracket, the higher your tax bracket, the higher your tax savings. And you get to build up your spouse SA and earn at least 4% interest.
You can get up to $15.3k tax relief by contributing to SRS and up to $8k tax relief for RSTU your spouse SA. However, SRS earns only 0.05% interest unless you invest SRS money to earn higher return, and spouse SA earns at least 4% interest relatively risk free. It is really up to you, and you can do both if you are able to.