My experience has been that the springs hang in there for a long time. You might want to try measuring one side against the other. Do this on a perfectly level (at least side to side) area. I don't know about the rear, but the front spring replacement is a challenge.
The new Bilsteins all around is a good decision. I expect that these will make you feel differently about your spring questions.
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in