I've never camped there myself, but you could try contacting the Central Highlands Regional Council (main office in Emerald) on (07) 49828333 and they will be able to help you out. Failing that, I do know that you can just pull in underneath the Nogoa River bridge (eastern entrance to town) and it's free camping. No power, but free just the same. Good luck!
We just passed through there and was told that the council had shut camping down at the showgrounds as it was not up their considered standard for camping. How ever there are two free camps, one at the AG grounds south of town and one at the Botanic Gdns under the bridge toilets are a short walk in the gardens. Get there early as very busy this time of year.
Rob and I stayed at the Emerald Showgrounds this time last year. $15 per night with power. Showers and Toilet fine. It was a busy weekend and the Rodeo was on. Had a good night. We stayed three nights i think.