I can see it being useful if you want to embark on a larger project but for most extensions that spans maybe 400 lines of code, well it might just be a little bit of overkill.
Good points all of you.
True, it might be overkill migrating a project to CoffeeScript, but on the other hand: for someone with limited JS experience, CoffeeScript might provide a bit easier learning curve. Speaking from my own experience, I've never really gotten the hang of JS properly - at times it feels outright hostile
I don't have nearly the same issues with CoffeScript though, so I guess a combination of the two is a good way forward (for me at least).
In the spirit of sharing, I put together a CoffeeScript version of Brian Munz' extension template. Works great.