I think the market has factored in the capital return as having...

I think the market has factored in the capital return as having wiped a full 80 cents from the SP (makes sense in theory, as the company has paid out 80 cents but has sold a proportionately valued asset). In reality, the real value drop was probably a lot less than 80 cents, as Sydney Airport really was the crown jewels in terms of income production. Over the medium term, I expect to see SYD recover around 40 cents, as the market realises the value of this stock has really not changed significantly. There may be concern over having all of their eggs in one basket (this is a valid concern), but if you were going to focus your assets on one piece of real estate, Sydney Airport is a good place to start.
I could be very wrong with my price prediction, but am not overly concerned as long as they continue to produce good dividends.