Well I've gone and done it, I've had the Autodelta 25mm sports springs fitted.
The wheels sit just right in the arches now, although the front could be a fraction higher. Overall it looks much more sporty and agressive, all 147s should look like this!
The ride is stiffer of course but still comfortable, it's a bit choppy over short undulations though. The handling has been tightened up to proper 'hot hatch' standards and does justice to the sharp steering. One worrying moment was when I was cornering quite fast and hit a rather nasty cats-eye which made the wheel leave the ground long enough to make it spin (the wheel, not the car!). I'm not sure if it was down to the unique circumstances or the new springs. I just took it down my favourite local road and it takes corners with very little roll, very controled.
Now to the not so good bits. The wheels tilt in a tiny bit, you have to really look at it from the back or front to notice. This shouldn't effect the handling that much but inside part of the tyre will proably wear out quicker. I think NumanRacing said you cannot correct this, is this true?
The main problem I'm having is speed bumps, my house is surrounded by them. The full length ones aren't too bad if you remember to slow right down, otherwise you hear a plastic scraping noise. It's the square lumps that are the buggers, I foolishly went over one with my wheels either side and I heard a rather loud plastic scraping noise. I tried with one wheel straight over the top and I heard a slight scraping noise, finally I went very slowly more or less down the middle of the road and that was OK. I've checked underneath for damage and it's not the front valance that's hitting the bumps, as I thought, it's some kind of plastic deflector under the engine bay. The back of it is cracked and hanging down more than it should. eek! Does anyone know how important this part is and how much a replacement costs?
Unless you are going to mainly use your 147 on track days I would recommend that you don't lower it more than I have.