Once you have edited the xlsm's you need to "generate all" in the all.xlsm file. The reason is that xlsm's are just for the looks - it is the relevant .txt that does the job!
This explains it pretty well!
Just a quick note - the XLSM file is just a workflow tool. Changing it shouldn't actually make any difference to the game. Instead, the macros in all of those XLSM files are designed to generate the actual TXT or LSX files that the game will use. If you don't have Excel or just prefer to use another tool (like Notepad++), you can still make the changes needed. Just need to know what files the XLSM macros do actually output.
Yes, in the other thread about treasure I tried changing the treasuretable.xlsm file and the drop chances that way. However, it did not seem to work, so instead I changed root templates (in editor). However, you can do a lot of different things using these documents. Such as:
http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Number=514998#Post514998 (Making new recipes and fixing older ones)
Modifying presets of individual characters rather than difficulty:
http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Number=510295#Post510295Editing individual spells and their affects:
http://www.larian.com/forums/ubbthreads.php?ubb=showflat&Number=510228#Post510228Just be sure to have a way to test it and confirm the changes ingame - don't just presume they happened (especially with main campaign, that one is tough!)
And you can do much much more.

Once you learned how to edit one of the documents and rest will come smoothly.