A Volvo isn't a softly sprung American/Japanese car that glides over bumps, so the 'bounce' test is not easily done. Even a 'bounce' of 1/2 inch on a Volvo is an indicator of a weak shock.
At 280K, your shocks are close to death. You may not notice it, having gotten used to the softer ride over the years. But when you get into a panic situation and the car doesn't respond like it should, the bad shocks can cause real problems in steering response.
Because the S70 doesn't have the expensive Nivomats in the rear, I suggest you get all 4 corners replaced with new rubber as well.

Klaus
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Proud owner of a 220S. If I had more room, I would have more Volvos.