Hi I've got a Subaru barely 20,000ks (IMPORT - please don't ask me to use warranty). Just noticed that - when fully loaded, the rear end sags, ie cannot see top of the tyre. Let's assume There's nothing wrong with the car or suspension, as it's stock and new, and that it is a load issue, the suspension wasn't built with carrying people and their things in mind.

What is the best way to fix this and maintain suspension performance? I know the cheapest way - fit stiffer springs. That means the shock and damper will be the same set up. 

Now if the stiffer springs maintain the car ride height when loaded, surely that "should" mean the shock and dampers would be working better than if the car was sagged?