Hindmarsh Island may have water views and what appears to be cheap water front property, but it doesn't have the swimming or surfing beaches like other towns near by, and it's the farthest away from facilities in the region.
The place also stalled mid development around 2008 giving the place an unestablished (and uninviting) look.
Then there's the obvious water issues.
Like a lot of other retirement/holiday regions the place has not recovered from the pre 2008 slow down.
The market there will probably perform well one day, however in the mean time I imagine the yields would remain poor, and CG no better than property a few streets back in some of the other towns near by.