I'd have to disagree, and since I have a 142 with cut front coils as a daily driver it should count for something.

I cut approx 0.8 coils off and had the end reheated and flattened. This was still not flat as factory, so I used a VW Golf (type1,2,3) rear ramped urethane spring seat. I didn't realize they came in pairs, so if you want a set of these, I will send the extra set for the cost of mailing. (email is linked by the little envelope symbol)

This will increase the rate more than you would theoretically think- I should have achieved ~10% firmer springs- I actually got more like 20-25% firmer springs. Why I don't know. I am only reporting. I have confirmed that the shocks and rubber bumper(lower) are not bottoming out.

To do this the coils have to be removed. If your car is aged underneath (ie you're from the 'rust belt'), this isn't a particulary pleasant job, and you should budget for all 4 ball joints and new bushings. (You in theory heat the springs in situ to sag them but this crosses the line between economy and hack, I.M.O.)

As the total cost creeps up as you add parts and labour to this job, it does seem more reasonable to look at aftermarket type progressives. You can go to V-performance, or you can take development in your own hands. The springs here on the bottom 5 rows (ignore that they say they suit rear): http://www.pitstopusa.com/SSS10.5REARCOILS.asp should work. Stock coils are 300 lb/in, so to go to a progressive a 200/450 might be a baseline.