Not aware of the leaf springs significantly weakening over time. You are probably fine with just new shocks. If your suspension has coil springs too then those are more likely to be the cause of sagging rather than the leaf springs.

Howdy KGV! Hope the weather is better in the MW than here in cold, dreary NE.... - 2 timing belts? Just one. Did you mean the serpentine belt? Good idea to change the serpentine belt at the same time as the timing belt. If the tensioner is original it should probably be changed too although those should last through 2 timing belt changes. The water pumps in these engines are robust and normally last 200k+. The timing belt interval is 70k. That is also the interval on my former 95 850 GLT. Same engine but one less cylinder. The very early 960's had a shorter interval. All that said, if the belt was last changed more than 10 years ago it should be replaced. Rubber deterioration....:)

jlvolvo - Look for timing belt change sticker under the hood. Or maybe you have repair records??