I can't imagine the rear end lowering after installing new springs, unless you had something other than stock springs in before.
If you like the lowered look, I suggest you replace the front spring pads from 2 bump to 1. If not then replace the rear pads from 3 to 4 to raise to front height as I do not think these pads give in over time.
My suggestion would be (c).
Just my .02
'91 300E, 206k miles