Hi. I live in Whyalla & see prop prices dropping here – probably because resources have slumped in recent times. Not a lot of other industry to keep things going. My advice to you is look at the rentals in each area – if there are lots then things aren't going well. If there aren't, & I would have thought closer to Adelaide would be doing ok, then look a little closer. More than 1 industry is good & that's why I would think Adel would be a good option. Also they're putting in the bypass from Gawler to the northern area of Adel for quicker access from the northern towns. People tell me Ceduna is doing ok, but I don't really know. Long way from anywhere else & fishing industry will face competition from mining (ie port access & pollution) in the future.
Good luck with your hunting – I always look around areas I know well, & haven't gone too far wrong in past 9 years.