I would leave your springs alone and, rather, buy thicker spring pads. These are rubber pads that go between the top of the spring and the spring perch. These pads are available in four different sizes, 1 being the thinest and 4 being the thickest. They only cost about $5 a piece. You probably need size 4. This would raise your car up enough to eliminate you scraping problem.
The other thing I would suggest is to replace your shocks with Bilstein Sports or Koni Adjustables. Because these are quite a bit stiffer than your OEM shocks, this alone might solve your problem. I have Konis on my lowered 190E-16V and when adjusted to full hard, these shocks really reduce the amount your car dips on bumps.
Hope this helps!
87 190E-16V Blk/Blk 5Spd.