We do slightly more clever stuff to export Excel, but on the import side, which is way less important to us, we generally fall back to CSV, as sad as that is, for the reasons you mention and more.
I looked at the Excel XML a few years ago and it seemed to take the inherent verboseness of XML and the inherent complexity of their binary format and melded it into a gargantuan behemoth of tag soup with a few bytes of real data buried in there, reliably extractable only with many hours of parser work and sorting through special cases. And it still didn't handle some things that the binary format did.
Don't get me wrong, XML is great and Excel is great and .xlsx is a move in the right direction. Just don't necessarily expect a nice clean chunk of XML to work with. Good luck!