I have also noticed that there is a distinct advantage to qualifying 18th vs 17th. This is clearly because you can save at least one and perhaps two sets of option tyres for the race, as Keke has pointed out.
It might even be possible to save all 3 sets of optiions and still qualify there although I don't think anyone has tried that deliberately although Webber did earlier this season. Just look at how many times in Fantasy F1, the 10 points you lose for missing out in Q1 means you get 20 points for making up the most places.
I think a tweak to the tyre rules would be better, eg giving everyone who makes it through each section an extra set of options. Something like those knocked out in Q1 have only 2 sets for qually & race. Those out in Q2 have three sets and those in Q4 have 4 sets?