Personally, even despite the fact I have "German blood," I'd rather play for the USA. No offense.
Are you first generation american? Like you have grown german parents who immigratyed to the US and had you there (then later on moved back to germany in your early teens with your family). If not, you arent comparable to Rossi.
Its nothing to simply decide by blood or the country you are born in simply, but its nothing to generalize either. I know your extremely biased feelings and I wouldnt want to restart a discussion I saw I side of you I dont like hehe, but its important to distinct clear cases from one another instead of brush it with the same stroke. Rossi was raised by italians in america, easy to identify with your parents culture and people first and foremost (laws and geography has little meaning to this)then instead of automatically only the country you are born in.
Thats different for example I presume, a scenario like yours, where your germanhood comes from centuries ago (or at most a century ago perhaps) of your forefathers immigrating to the US. I would assume like with most of long ago immigration, your family has long ago lost whatever tie there is to germany culturally and in other way, except by blood and perhaps name. That they are your average culturally typical americans, with all ties to the country, and little if any to the old world so to speak.
Not saying you were comparing, but you realise how different these cases are and how in general its not good to brush them with the same brush? Your sitaution (if I presumed correctly) and someone like Rossis are quite different, and has very much different factors in taking a decision choosing one over the other, you would be unlikely to have feelings for germany, he would be likely to have strong ones for italy (its a choice those who have double choices like that has a right to make, like how Balotelli made his for Italy. He most likely feels zero ties with Ghana because he was raised by italians in Italy, instead of Ghanaians in Italy).
Just like for example my swedish friend who is of french origin of long long time ago, feels fully swedish and has little to do with france, cant be compared with for example my little brother who is born in sweden but still due to his family and everything else, totally identifies with his origin of Somalia, even if one is a product of sweden too and is attached to it. Both people who are legally swedish citizens, and both love it, but also has very very very much different relation to their origin and ethniticy.
In relation to this thread, if Amauri even has 25%(we dont even know if he has at all) or 100% ethnic origin to Italy, he would most likely a case similar to you in having zero feelings or ties to Italy. While it would be different with cases like Rossi etc.