I was reluctant to answer directly for the OP, and have probably already posted enough on this topic, but thought your question about domestic spying disingenuous - there are plenty of examples of things people might be upset by, and no need to ask for proof of US domestic surveillance - we probably know very little of what goes on ('the tip of the iceberg'-L. Sanchez), and what we do now know is shockingly extensive.

Personally as a foreigner my opinion is probably unimportant to you, but I don't think the NSA should be attempting blanket surveillance at all, foreign or domestic, whether data crosses borders or not - there should be public courts deciding on each request on an individual or organisation, with search warrants granted where it is deemed in the public interest, connected directly to an ongoing investigation - decisions could be kept secret for n days. What I would allow are tapping of all devices/contacts for a single person over an investigation. This would dramatically limit the effectiveness of the NSA by design. The most effective spying or police agency is one with a camera in every room and a tap on every phone - that's not a world I want to live in, and I see no problem with limiting their effectiveness, just as we ban certain arms from warfare because they are indiscriminate and awful in their effects.

I also think the analogy with pen registers that you are drawing is not appropriate given the advances in technology meaning data can be mined and kept for lifetimes, collated, and cross referenced globally in an instant. That's an entirely different world of surveillance, and one we are just coming to know. It makes old distinctions obsolete, and demands new rules for a world without frontiers - borders are now permeable, whether we like it or not, and they don't have as much meaning as they used to.

Your argument about data crossing borders is a great example of this. So many Americans use services overseas and vice versa that drawing some distinction between foreign and domestic traffic in this world is meaningless - if you say things that cross the border are fair game, you're giving the NSA power to perform dragnet sweeps of virtually the entire world, as virtually everyone's data will cross borders as some point in its existence. Imagine an American company with London offices - suddenly all their correspondence is now acceptable for surveillance without a warrant.

Mining global internet traffic and telephone metadata is extremely dangerous and potentially wide-reaching in its effects. It could easily be used to reveal any journalists' sources (no more free press), politicians' past affiliations private or public, people's donations, health details, reading preferences, purchases etc. Worse than that data collected in 2001 could be used in 2021 by a hostile NSA director against annoying journalists/rivals/judges to destroy their career for some sexual peccadillo irrelevant to their professional work. To have that much data collated on someone over a long period of time is very dangerous - for the person concerned, and for the organisation which does so. I simply don't trust any one organisation with that sort of power.

So I'd draw the line a bit closer to personal privacy and public transparency than the OP I think, but that's ok, it's great to have this conversation at last, and we have Edward Snowden to thank for having a little more knowledge with which to do so.