I replaced the front suspension in my Mazda 2. It was bouncing all over the place. I ordered new shocks and springs, bump stops and dust gaiters.
When doing this I found that one shock adsorber was totally knackered. The other side appeared to be fine, but I still replaced it. The springs looked fine, the same height as the replacements, but I still replaced them. The gaiters were completly knackered on both sides. When doing the job one of the strut top bearings was in a right state, but I never ordered these parts. So I've had to take one side out again and replace that. I've also just done the other side today as I'm a bit of a perfectionist.
I guess you learn from your mistakes, just replace everything and do it once. The car had done 59K. It's a much better drive now, well as good as a 1.3 Mazda 2 can be..