Dear Mark,
I think I don't have good news for you.
The BW 3.X addons are not supported (SAPGUI 7.20 included) since April of 2013.
You should not use it, a long time ago.
What you need, is an BW Objects upgrade (that means queries and workbooks) to version 7.0.
So first. Excel 2013 and BEx Analyzer 3.x is not compatible and not supported.
If you have any issue with BEx Analyzer 3.x, SAP cannot provide support for you.
Regarding migration:
The migration of Queries and Workbooks are quite simple.
For queries, you have to open the query under Query Desginer 7.0 and save it. (I recommend you to use Business Explorer 7.0 for SAPGUI 7.30 --- Do not use for SAPGUI 7.20).
For workbooks, if you have, it is the same process. Open with BEx Analyzer 7.0 and save it.
The version of Excel is irrelevant on that procedures.
For Web Templates, has some extra steps, but I do recommend you, if possible, consider to recreate these webtemplates under Web Application Desginer 7.0
Best Regards,
Edward John