Redline isn't an issue with the 4C. If a driver does rev it out enough to hit redline, one of two things happens, both are classified as 'self protection'. There's many variables involved here.
1) It will upshift into the next gear.
2) The rev-limiter will kick in and shut off the fuel.
I've experienced both without harm to the car. I prefer the upshift rather than the fuel cut.
The sill, rocker panel, rear fender are fiberglass and repairable depending on level of damage. The rest of the panels ore SMC and not repairable. I have no knowledge about the engine hatch.
Body panels are the least of (my) concerns. It's the mechanicals that hold the wheels on and so forth that are important to me. The car doesn't need the fenders in order to drive, turn & stop.
Back to the insurance company and their thinking. First, it starts with the body shop or dealer or repair shop that does the repair estimate. For an insurance job, they don't repair any parts. They replace everything that has even the tiniest mark. That $6,000 dollar panel that might be repairable for $300 and some paint, gets replaced. The replacement panel will still need to be painted.
Then there's the unknown decisions the service writer made. Perhaps only one control arm is bent, but he/she wrote it up that the entire corner gets replaced. One control arm turns into upper and lower with a knuckle and bearing set and a wheel. Without actually doing the technical work involved to know what the truth is.
When I crashed my 4C, the repair was out-of-pocket. The estimate was $20,000. I got it down to $15,000 because I refused to replace every nut, bolt & washer that had a spec of flyshit on it. Does it effect the mechanical safety of the car? Can I see it from a normal viewing angle?
The carbon fiber tub can't be fully inspected until the car has been disassembled. I doubt they took the car apart, inspected it, and then reassembled it with the bad parts. There is that, "fear" factor. There is the $$$ involved just with the obvious.
Congrats and good luck.
2015 Alfa Romeo 4C