Subaru Impreza STI 2007: The harder they come...

You can see Subaru's point. Being an individualist carmaker in an increasingly uniform world is a battle you're better off not fighting. Your mainstream model is a car with a choice of a boxy saloon body or a five-door that's not sure if it's a hatchback or an estate car. The doors have no window frames. The engine is a flat-four (the only one of its type in production) and it drives all four wheels. That's hardly going to sabotage sales of a Volkswagen Golf, is it?

So, you reinvent your mainstream model, the Impreza, with a five-door hatchback body – a body with a strong hint of Mazda 3, but with a front-end design that is both nondescript and inept. You give it normal doors and a hard, plastic interior that is even cheaper-feeling than the old car's. You do, however, keep the flat-four and the four-wheel drive, because it's your USP and now the only reason why a mainstream buyer would consider your car over something else.

This is all fine, possibly. But there's this hard core of car nuts who've built a petrol-headed cult around your fastest, maddest version: the Subaru Impreza STI. Historically, it has been expensive because of the sophisticated four-wheel-drive, turbocharged engineering, yet its cabin has always felt cheap. If this cult-soaked semi-supercar is to find more buyers, its appeal must be broader.

The basic Impreza is now squarely positioned as a mass-market hatchback. But at an event for the new-generation STI, held at the Mount Fuji race circuit, the marketing presentation was sprinkled with pictures of cars such as the BMW 130i and Porsche Cayman. From mainstream hatch to premium £25,000 plaything, while keeping the STI loyalists onside – to pull all this off would be quite a feat.

Here at Fuji, the mountain looming in the mist, there's no doubt that the STI has retained some of the visual character that the regular Impreza has now lost. It's the usual STI stuff – broad, outwardly extended wheel arches to cover wider wheels, a big air scoop on the bonnet to feed the intercooler, deep balances with foglights set in cooling strakes, a rear spoiler. And four exhaust pipes, when previous STIs looked coolest with a single big one.

Open the door, step inside. The seats are suitably snug and supportive (I'd recommend the optional Recaros if you're planning, like many STI owners to date, to head to a racetrack), there are some intriguing new buttons and switches, and, at first glance, the interior finish looks promising. Then stroke the dashboard or the doors with the back of your hand, and discover that the promising-looking matte finish is so abrasive that it has removed some of your skin. So much for tactility. And so much for marketing.

I go in search of bumps on the circuit's access roads, to discover suspension of surprising suppleness compared with previous STIs. This might be a good appeal-broadening measure, or it might spell death to the STI's hard-edged soul. Now to the track, to find out.

There's a new system called SI-Drive that tailors the accelerator response according to perceived need: making it mushy and gentle for heavy traffic and emphasising the turbocharger's response lag, but sharpening it if you suddenly demand power. There's even a change-up light to help you get the best fuel economy. It's good to know your market.

Or you can switch to Sport, which makes the response proportional to accelerator movement, or to Sport Sharp, which exaggerates the effect of the first part of the movement. This last is best, because it gets the turbo working more quickly, and it's not too tetchy for normal driving. It's the obvious setting, and makes the others unnecessary. More technology we don't really need.

UK-market STIs (on sale next spring) will have a development of the previous car's 2.5-litre engine, now with 300bhp (instead of 280) and 300lb ft of torque; the improvements were achieved by fitting variable timing to all four camshafts. My Fuji mount, however, is a Japan-spec car, virtually the same as a UK one except that, for tax reasons, it has a 2.0-litre engine. Despite this capacity shortfall, it produces both more power (308bhp) and more torque (311lb ft), these peak values arriving 400rpm further up the rev range. Inevitably, response from low speeds suffers, and with its twin-scroll turbocharger and altered exhaust system this STI doesn't quite have the deep, throbbing beat that is a fast Impreza's aural signature. We are promised, however, that UK cars will have the authentic sound effects.

On the track, the STI feels fast (0-62mph should take around five seconds), but the usual hot-Impreza pointability and driftability seems to be missing. Has it gone too soft to appeal to a wider audience?

Time to play with the DCCD, or driver-controlled centre differential. In Auto mode, it constantly alters the torque-split between front and rear axles to give maximum stability. But that's not necessarily what you want on a track. Auto Plus makes the STI even more inert; it is meant for very slippery surfaces. Auto Minus "loosens" the centre differential so the rear wheels get more torque, more of the time. That's better: it's starting to feel more like an STI now. Still, that raw edge of interaction, that feeling that you could tease the car into all sorts of different cornering styles and it would play along, is missing.

It's time to override the technology – something you didn't have to do with the previous STI's broadly similar system. So, ESP stability system (which Subaru calls VDC) fully off; DCCD to manual, tabbed back to maximum rearward torque bias (59 per cent); and two more laps of the fast, sweeping Fuji circuit.

Thus, the STI's character re-asserts its presence. It feels like a proper, driver-focused, four-wheel drive wonder-car again, letting you drift the tail but always pulling itself straight when asked. I can use the power to point the nose at a corner's exit; I can enjoy this STI in the way that a Subaru STI is meant to be enjoyed. The new look and the new toys are distractions to what is still a great driving machine with a shoddy cabin. Beneath the marketing muddle, it looks like it's business as usual.