Sick of my crabby lawn.

I live on the Sunshine coast, very very sandy soil without much nutrition in it I think. I have lots of what I think is paspalum that I periodically attack but at this point there's not much left under it that isn't paspalum. Then there are patches of ?couch and maybe even kikuya, I'm no good at telling. What do you guys think? Should I kill all and start again? Any selective herbicides you'd recommend?

From above

What's this??