Ride quality on coilovers is 1000x better than springs (I know, I've had both) because the shocks are matched to the springs therefore they absorb the bumps in the road etc. much better than just springs.
If you fit springs alone, its just like fitting harder, compressed versions of your standard springs, and unless you fit shocks aswell, your standard shocks will struggle to absorb the bumps in the road, and you will find yourself bouncing down the road, being able to feel every little stone in the road as if it were a crater and just generally being uncomfortable.
My coilies are down about 80-90mm and even at that height the ride quality is soooo much better than when I was on 60mm springs, looking back now I don't know how I put up with it.
If I was to do it all again, I wouldn't bother with springs and would save for some coilovers. Seriously can't recommend them enough to anyone wanting to lower a fair amount.
Just my 2p worth anyway...