Air Asia BIG is one of the worst rewards values out there: you earn about 1/2pt per $ and they are worth an average of about 1/4 cent/pt, so you'll roughly get less than a 3% reward rate, or half what Cebu Pacific or the US3 do.. but better than nothing... you can find the analysis
here
Values vary greatly, but the fixed fee rewards can be good value when there are no promos or you are booking late.
if you're getting 0.25 cent / pt from $2 spending. I guess that's not 3% reward rate, that more like 0.125 %....
Their points doesn't worth anything, it's more being there so you could be one of the first to access their promotion fares.