If American laws required a full financial disclosure of spending and investments in America,would the church comply if there was nowhere in the world to hide this information?
I believe that it would, because it complies with financial reporting laws in other countries such as Great Britain and Canada. The trouble is, with the current political climate, there is little collective will in the U.S. to require greater financial accountability from churches.
My personal feeling is that any organization that benefits from a charitable exemption from taxes, and takes in more than a given amount in donations (say, 50K) should be required to report its financials.
Many churches and denominations do so voluntarily. If you do a web search under "Presbyterian church budget," "Methodist church budget," etc. numerous examples will pop up.
The church hides all of their financial dirty laundry in the US, away from the eyes of everyone, on tax returns nowhere. If the US suddenly required tax returns from the Mormon church, the apostacy rate would increase dramatically, immediately following the publication of their first published tax returns. Too many lies and financial mis-appropriations would be revealed.