Excel never obfuscated their save code. I've seen it in person. They did just memcpy their data structures, which was the most efficient way to save on tiny machines of the day. Lotus did that too.

I've also seen and helped implement the Open Document spec. This is not a simple problem and you are doing yourself a disservice by blinding yourself to the scale of the task.

If you want to make an impact and don't have Google level budgets then leveraging OpenOffice is the only sane approach.