as I owned a 156 GTA and now drive a 3.2 brera (still in my first week) I feel I'm qualified to comment. The 156 is quicker, the brera handles better - it's like it's on rails.
The brera is a smaller car all over (front, rear and boot), although it's got a 60:40 rear seat to make the boot larger than the 156's, but weighs more. The fit and finish on my pieno fiore leather is brilliant - and apart from the passenger seat rocking when empty I have no rattles or noises to speak of.
The v6 noise is not as good on the brera, and the mid range urge on my car vs/the gta (bearing in mind the cars done 230 miles) is not the same. Again Fuel economy is initially worse 20mpg vs 28mpg - so I hope it's going to get better... I can see single figure mpg's on the trip in normal driving when I used to have to hang the balls out on the GTA to get those, but we'll see as it develops.
Is the brera a better car - yes, is it a GTA - no..
Question is with the SV costing 29K plus options add a pair of turbos to the 3.2 for the GTA plus added lightness - will the GTA have the tintop roof for lower weight?? I think you're talking high 30's list. That's too rich for me.
Alfa V6 - the ultimate aural pleasure
Simes - the Alfaowner formerly known as Alfa156man