"So let's say I live in Germany (I don't :-P), and you live in the US,"
We have different issues here. One is data knowingly shared with a US entity, which may also be mandate by law to store them, as sales invoices.
Another is personal or business data not shared with anyone, but stored on systems owned or controlled by a US entity outside US.
If you send me an email and that's stored in the mailbox of a US citizen on US soil, a valid warrant to access that mailbox will access the emails, and it couldn't be different. I can't see how it could be different from a paper mail or a telephone call.
Just, if a US law enforcement agency believes you, in Germany, could be an accomplice, and more evidences could be in your mailbox, it should not be able to access your mailbox but following existing treaty and procedures to ask Germany to help in the case, regardless of who owns or control the system.
If I buy something directly from a US based entity on US soil - say an AR-15 from NRA'r'US - that record will be accessible by a US investigation wit a valid warrant to inspect company records. Just, if they need more data about me because I bought an assault rifle (I know, they are usually OK with that, just an example), they shouldn't be able to ask any data stored on any system a US company may have access to wherever it is. Follow the rule, and ask Interpol or local low enforcement agencies and courts. And don't try to abduct me illegally as CIA did in Milan.
If I buy from Amazon EU based in Luxembourg - I do expect my data aren't available directly to any US agency at all - OK, I know NSA could access them illegally, but that's another matter, they want to be able to access data legally so they can be used in courts without the hassle of going through foreign paperwork and have to talk to those people with all those strange languages.
If I have a safe box in a bank in Germany, even if it is controlled by a US company in some way, I can't see how a US policeman could enter and ask to inspects its contents with only a US warrant. Or if I live in a German rented apartment controlled by a US company, could they enter it with a US warrant?
The actual legislation may be inadequate to cope with data shifted continuously across datacenters - surely new treaties and legislation is needed, but it would be much better it US didn't try to act like the 800 pound gorilla, and look for an agreement that lets domestic investigation proceed, without putting in jeopardy the sovereignty and rights of foreign countries and citizens.
Making enemies if far easier than making allies.