I know what you mean about the classy look, think Maserati rather than Need for Speed.
The 147 is built on the same floorpan as the GT and also shares lots of bits with the 156. Wheel PCD is shared also with the GTV/Spider from the previous gen cars. Don't worry about wheel fitment and offset, any Alfa rims will either fit or fill your arches a bit. GT Black line wheels are nice 18 inch jobs, so are Ducati Corse alloys. The GTA multispokes and teledial rims also look really nice. I'd go for 17" wheels because the ride will be crashy on anything bigger.
Zeatek do an aluminium undertray which is sold by alfisti.net. They have a huge range of tuning items on there and the lower VAT negates international delivery if you buy things together.
The Cupra R splitters have gone up in price to £45 at the main stealers so grab one here before they go:
Red Hammerite direct to rust paint is the ticket, available for under £10 a tin. Other than that, the Brembo's from the 166 can be had for peanuts and will fit with a bracket and redrilled discs.
Badges can be had on:
Partsworld-UK home page
Exterior Trim and Badges for Alfa Romeo 147
The Alfa Workshop, specialist Alfa Romeo garage and web site
and Alfa Romeo Shop - Tuning, Styling, Fanartikel und Modellautos
Other stuff that you can modify includes blanking off the EGR on a JTD for more power and engine longevity:
You can fit 15mm spacers all round with 17" wheels for a nice full arch (or fit GTV wheels which have a different offset from the outset).
You can delete the DPF and both cats (downpipe & main cat) on a diesel and replace with shiny tubing:
You can fit a tuning box to a diesel for more mpg and more Oomph:
A strut brace will tighten up the cars nose, it takes half an hour to fit and is the best £100 you will spend on handling.
Eibach springs will lower the car by 10mm. It looks lower than that tbh so bear that in mind if you consider them on that basis. It might look faster but you'll be lots slower over speed bumps! Consider uprating the shocks because they are renowned for being soggy at low speed and nails at high speed.
Consider instead, uprated Eibach ARB kit which will reduce roll without compromising comfort.
That's all for now,