It depends on the weather as to the amount of people. Most people stay south up to Happy Valley.
I have been going up at easter for 2 weeks for about 10 yrs now, we go north of dunduburra. On average it is usually quiet with only half a dozen campers over the 4 day break, no one after that but us. Weather is usually blowing out of the South East with Showers or rain, Think we have had 1 fine year.
If you are going inland to the sites then either do it really early or late otherwise you will get no parking close to anything, and the tourist busses / backpackers who cannot drive if they tried , are a pain
cheers