How did they come at that quote given they are $19,990 drive away? (there are plenty on Carsales for $18,990 too but they might be MY15).
From my experience selling a MY10 i30 at 5 years and 140,000k, no one looks at the year, it's all about the condition.
If you look after your car and keep it in excellent condition, no one will be looking at the MY because they will be too busy telling you how good the condition is (at 5 years there will be plenty of knocked around ones out there).
Good condition/tyres/rego will trump MY every time (unless there is a major change which MY 15 to 16 there is not or at least I can't find anything).
The big change comes later this year when the new model comes out, I think price and not goodies is doing the heavy lifting until then.
Personally when I buy a car its about minamising the cost per km. Depreciation happens from the cost of the car less the sale price at disposal. The up front cost is by far the bigger number, so anything you can do to reduce that number will have a bigger effect on the cost of ownership, even if you can jag an extra $500 for MY at the end (which is doubtful, especally if you keep your car for longer and sell privately).
On that point, you can get a MY 16 Kia Cerato for $17,490