Removing the helper springs is fine, BUT, your MOT man might not like it. All they really do is keep the spring located when you raise the car off the ground which I'm pretty sure is a fail if they don't.
I had mine at the bottom of my spax RSX coilovers, with helper springs still in place. I had about an inch between the lower anti roll bar and the ground. It would catch on quite a lot, Most speedbumps were a Big NO.
A few things to bear in mind,
Exhaust centre box hit first, on things I wouldn't consider to be particularly high, followed by the sump, sills, the front wishbone mount seam, ripped an anti roll bar clamp off in a small pothole, Lower front strut brace, front "splitter" part of bodykit etc etc. It killed CV joints pretty quick, and got through a pair of wheel bearings in about 18 months.
The ride on the road was also terrible, any bumps in the road would launch me up out of the seat if I hit it at a decent speed, Great on a nice smooth track but not fun for everyday use, although I'd put this down to being sat JUST above the bump stops so any suspension movement meant it was hitting them. Shorter ones would definitely have helped though.
Ended up going a bit higher for my current set up, mainly due to the alloy sump on my engine, Don't really want it cracking. At the moment it sits with the top of the tyre Just level with the arches. 15" wheels and a 55 profile tyre.
Don't think I'm trying to put you off, A LOW rocco looks awesome, but can get expensive.
All that being said, I am seriously considering getting the C-Spanners out and bringing mine down a touch more.
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See winstons build thread if you want some ideas about going mega low.
Ben.