Thank for your inputs.

Well, i drive quite gentle, never hit speed limit, speeding corner, accelerate in the middle of turning or else.
And actually after changing the tyre i did went from Sydney to Wollongong for a day trip and noticed no obvious difference.

I just want to be clear about the trade-off between safety factor (we're expecting a baby) and the financial side of the story to found out is this worth or not, to change to two new tyres, put one on spare and get rib of usable one >"<.
It could be a lot easier if our budget isn't so tight ^^!