I had an ST170 and it was a great car. There's faster stuff out there but as a warm hatch for the daily commute it was pretty cool. Its like someone above said, they're fast enough when your last set of wheels was a 1.8. Personally I wouldn't bother with modifying an St170 as your gains will be minimal, unless you switch to lairy cams and throttle bodies, but then it gets expensive so u might as well switch to something with a turbo. Mine was standard, but a mate spent a fortune on cams, filter, exhaust and a remap and he gained summat like 15bhp for around a £1000 - £1200. The engines are so highly tuned from the factory in N/A guise you wont gain much.

The talents of the car are pretty subtle, if you go hurtling round Windemere in one you'll kinda twig on that the power is really well balanced to the grip and suspension. I did get bored of the power at times, but down back lanes the 6 speed box kept the power in the VVT band (between about 5-7k rpm) and stuck like shit to a blanket. Mine was a bit temperamental, needing work every 6 months for something or other, like brakes, ECU warning light, tyres, all sorts. But i'd buy another, it was easy to live with, fast enough to be fun, ok-ish on juice. The interior is just a focus with half leather seats, its not that exciting, have a look at one and see what u think i guess.

But yeah, you will get bored of the power eventually. Its only on track days or down country lanes that the whole thing comes together I think.