I had a 03 st170 for about 2 years. Put a k&n induction kit on and a custom cat back and put 30mm lowering springs on. Also had to get a new set of wheels for it as the original ones were badly corroded and pitted.
The handling was awesome on it!! Probably one of the best handling cars I've had. I've got a fabia vrs now on coilovers with a RARB and I would still pit the focus against it around the bends.
The power of it was shocking though,couldn't be driven over 3000rpm due to the fuel consumption so was pretty much limited to 70. I wouldn't mind the fuel but it wasn't particularly fast, now a new shape st I could live with the poor fuel because you've got the power but this was ridiculous.
The tax was expensive for it also. The clutches are dear and I had problems with inlet manifold.
Would I buy another? No probably not due to tax and high fuel bills but do i like them? Yeah they're nice to drive if someone else is going to pay for the running of it. I think the trouble is I now have the fabia which I can tax for a year for less than I could tax the focus for 6 months. I can do 600 miles on £65 of diesel getting approx 55mpg so the st170 just seems obscene to run in comparison, I was getting 350 miles on £70 driving at 70mph whereas I can cruise at 80 easilly now. Not slating them I do genuinely like them just too costly for me for the performance.