I'm really OCD-ing out here and I'm manually doing things right now
You shouldn't invest time in manually editing those files ! ;-)
Excel 2007 is fine to run my VBA code.
Let's proceed in steps with development:
Create program to parse existing txt files and generate separate "per game" xml files + global gamelist.xml.
Parsing requires source txt to have a defined structure.
Looking at those TXTs the first part is ok (assigning specific fields/tags value).
Then, after the"----------" there's the description. Last line always contains info source reference. Is that correct ? if so I will use these "rules" to parse the files.
Add customizable folder paths (preference settings) that will be used during xml generation. In this way people can have supporting files in the folder they prefer.
If I understood correctly for each game the rom name has to be added as it is not contained in the TXT file. All extras (boxart, video etc) are then named the same as the rom but, of course, with different extension and path.
This can be generated too by the program.
For existing XMLs (work you have already done) the program would read-in just the rom names and combine them with corresponding TXT data and generate XML.
I suppose some games will not have some of the extras, so generating ALL EXTRA tags would actually create some "broken links" to missing data. Not sure if that would make ES "unhappy" and generate an error or if ES just ignores this.
Concerning the case issue the program could simply generate all lower or all upper case.
In this way you just need to "case convert" all actual extra files accordingly. I'm pretty sure free windows utilities exist to do this.
I'll be away over the next days but can start working on it this weekend.