I thought the same thing but apparently there is a difference. Crumple zones stay more-or-less intact and absorb energy over a relatively long period of time. Shedding parts removes the energy in a hurry. But I don't grok all that (it makes sense going by what I remember of my Physics classes but I can't say I fully understand it), so take it with a grain of salt. I'm assuming that the guy knew what he was talking about (he was a 2nd generation body guy) but you never know. ;)

My 2010 NISMO was involved in a front end collision last November. Didn't get my car back until end of March. Had to return in 3 times for problems. Even then the car was never the same. Sold it, bought a corvette and haven't been happier. The one thing you have to remember you will lose a good deal of money on the sale of the Z. Z's already have poor resale value, add an accident to that and it goes down more. My Z was sold with a perfect carfax and everything, but it was easy to tell there was body work to the car by the appraiser. Given your situation and where you live I'd definitely go with an STI. Or like someone else mention, sell the Z, pay of the fiat, drive that for a bit and then move on to something else later.