Springs or not to Springs - 1991 W124 300D

[Bengoshi2000]

So,
My plan to do shocks/struts back in the fall did not come to pass. I've been carting the kids back and forth to school but hadn't put 4 "healthy" adults in it before last week. Seems the entire car sat 2 inches lower... or more in the back it was riding really low. So now I'm thinking I should do springs as well.

My questions are straightforward:

1) Given the age of the vehicle would new springs be any benefit?
2) I've read that there were "taxi springs" available for the w124 rear and I'm interested in the possibility of installing a pair... assuming I can find a pair.

I'm convinced the shocks/struts are gone along with the strut mounts. Front right squeaks like a donkey in heat. I'm going to bite the bullet and do the rear multilinks at the same time.

Peace,
Norm