My first job out of college was converting all the Excel spreadsheets that ran the business to web apps so I certainly know how they are used, and more importantly, how they are abused.

If Excel had a real scripting language as it's Macro language the problem wouldn't be nearly so bad. All that business code could just be copy/pasted, have some unit tests implemented then refactored so that the accountants code is now updated by the developer. As it is now the code has to completely rewritten in a new language.

As for the language choice, VB.Net or C# would be fine. I'm not saying it has to be Python. My complaint is that the code is non-transferrable. The apps cannot grow past Excel, and the email the most recent version to the next guy game gets you into versioning hell rather quickly.