I haven't stayed at the Rodeo Grounds, but know the Atherton Tablelands quite well. I notice that they are also calling it the Cairns Highlands these days too. I agree with Jon that Mareeba is a good base. The Kennedy Highway from Mareeba to Cairns is the best/easiest 'down the mountain'...as opposed to the Gillies and the Parmeston Highways.
Personally, I don't like Cairns itself very much, very busy city, but the scenery in the Highlands and along the coast is amazing.
Been to Cairns a couple of years ago and stayed at Crystal Cascades C.P. It is out of town about 6 kms but it did not worry us at all. It is the only C.P. that we have stayed in that changes it shower curtains EVERY day. Cleanliness is of the utter most importance. Owners, Janine and Russell are very friendly and very helpful. While we were up that way, I finished up in Cairns Hospital and could not travel for 2 weeks, so went back to the park and they helped us by squeezing us in. We were very grateful.
Was down at Mission Beach and Kurrimine Beach yesterday and the Caravan Parks are starting to fill up. Great to see. Hopefully there's some of the GN's from this forum staying in the area.