Valinco, you comment that the GTA will hold its value better than the more common GT but they are all around in only tiny numbers, I do appreciate that the GTA may have more investment value due to its badge '
However, look at GTV V6 values lately, I'd suggest that anything , be it GTA 147, 156, GT or GTV will be a solid investment for the future as their numbers can only go down over time.
Marky, just another thing to consider with the Brera is the weight penalty, they are a heavy beast and this will have an impact on the handling and enjoyment.
worth test driving each model you're interested in to see the differences for yourself
Good luck with the search, bud