This seems like the type of question that would be a good use of the (disputed) practical-islam tag. I would say that such questions would be on-topic, but it would need to be written in a constructive manner.
Any such questions would be at high risk of subjectivity, or of soliciting a lot of equally valid "answers" (read: opinions). The canonical blog posts on how to write a good subjective question can be found here:
While completely reading these two blog posts is highly recommended, for the sake of this post they can be effectively summarized by quoting Aarobot: "real questions have answers, not items or ideas or opinions."
To bring it back to the direct topic at hand, your example question
How can I earn money in the USA and save it without breaking any islamic or USA rules? is far too general to be constructive; there's literally an infinite number of ways you can earn and save money thus. There are no criteria to determine exactly what distinguishes a good answer from a bad answer. I could tell you to dig empty bottles out of trash cans and hide them under your mattress, and it would be perfectly valid as it lets you both earn, and save, money legally.
That's probably not what you want.
On the other hand, specific questions about whether any one particular activity is an Islamically-acceptable method of earning and saving money are perfectly fine (the business and investment tags have a number of such examples).
Again that's probably not what you want.
Unfortunately, from the example question, I can't exactly tell what you want. That's one of the down-sides of having such a general question in the first place: people who write answers need to know what you want in an answer, otherwise they risk wasting their own time — and yours — giving you answers you don't want.
A good question is defined by its answers, and especially defined by the answers it expects. You know better than anyone else what you want, so to write a good question, you need to write it in a way to attract those answers in particular, and exclude those answers you don't want.
In short: Should general questions be allowed? Yes, but only if you can make them work.