Suspension Dampeners SEAT Ibiza IV Hatchback (6J5, 6P1)

I have recent lowered my Mk4 seat Ibiza by 45mm front and rear with some lowering springs however the back of the car is not as low as the front and I would like to lower it more. Obviously cutting the springs is a bad idea. 

I have been thinking that I could very easily lower the single rear axle on the rear by removing the rubber dampeners/shims/bushings which sit on the top of the spring between the chassis where the springs sit on either side. I want to know whether this is a good idea? I am not sure the purpose of these rubber bushings as they are very stiff, with not much give in them to improve the ride and they are about 50mm in height. The springs would sit comfortably on a little nobble protruding from the chassis which the rubber shims usually sit on but am I likely to cause damage with the springs being metal on metal? Would it be better if I perhaps use a thinner bit of rubber to still get the lowering effect? Or is it best to just leave them all together?