Use the Profile fields for the extra data and then use Advanced User to filter and page through the data. Not a spread sheet but it is an alternative solution. The Profile fields can be set so that only administrators see the data.
I think 'spreadsheet' is a requirement, but thanks for the pointer.
Don't know if it is what you are looking for, but Ajax Table was good for my site to manage nodes.
Very interesting. I will try to convince the boss. :)
Thanks.