I've only had my 2.4 SW about 10 months, so not as much experience as a lot on here, but there's no doubt it's a front heavy thing. It's a bit of a handful at low speeds driving around town, things such as 50m run, junction, 30m run, junction etc. A remap helped with a few less gear changes, but it's still not great. However, the trade off is when you get it up to some decent speed, it feels beautiful then, really surefooted. I always find it's nicer with a fullish tank of fuel in the back, it doesn't really make the car feel heavier because there's so much power. Some say the Powerflex stuff helps out, but it didn't work out for me.
I think if you found your 156 front heavy then a 2.4 159 would probably be worse, my 1.8 156 was great around town,(barring suspension), it was also great at 90mph, it was really the lack of power and the want for a 159 that made me change. I think a lot of people would be happier with a 156, it's just it's an older car.
One thing that gets me is how the 159 gets a slating for it's weight when the current crop of 3 series,C-class, A4 etc are all way heavier. The thing I absolutely love about the heaviness of the 159 is that when I get in the GT V6, it feels like a Go Kart, the steering is so light! But you know the steering on a 3.2 isn't actually light at all, so it shows how heavy the 159 2.4 is at the front.
GT 3.2 V6 - Q2, KONI FSD & EIBACH PROKIT, GTA REMAP, MICHELLIN PS3's, BMC CDA
159 SW 2.4JTDM TI - ALFATUNED, WIZARD BACK BOXES, KW V3 COILOVERS, NOKIAN WR A3/MICHELLIN PS3, PCA DYNAMICS ALIGNMENT.