Hi Rob,
We currently have two tools for bulk editing XML files - our command line tool (which does work against SharePoint libraries) and our InfoPath tool (that works with XML stored in SQL via our DBXL Web service). We are planning an Excel-based tool for our next release (v2.3) to provide "data sheet" functionality for editing forms. We are also building tighter integration with SharePoint for our DBXL product so you will be able to easily move your XML files to DBXL and still use SharePoint to open/edit/view them (even though they live in SQL).
We recently removed the command line tool from our webstore but we would be happy to show you how to use it and enable it for your document library. If you are interested, please purchase one Support Incident in the web store of our sister site, Qdabra.com: http://www.qdabra.com/products_all.asp?cat=12 . We'll throw the tool in for free. Of course, if it doesn't work, and you aren't completely satisfied, we'll refund your money.
Your second question was about creating new InfoPath forms. We have an XLS to XML tool that lets you use Excel to create multiple XML forms and these forms can be uploaded to SharePoint. This is a batch tool. We would be happy to also show you that tool as well. It is currently for sale on our webstore: http://www.qdabra.com/en/products/ExcelToInfoPath.aspx
Finally, if you are interested in the next release, and you can wait 6-8 weeks, we'd be happy to have you as a beta tester. As a beta tester, you can qualify for a big discount on our tools and time. Please let me know if you are interested.
Best regards