On one hand, Notre Dame is an important historical building, even if you only looked at the art and architecture; and yes, even it's religious history adds immensely to its important, as that reflects the impact it has had on history, and this is coming from a very non-religious person who appreciates history. Given all of that, I would be very much for whatever can be done to keep it in as great a shape as possible, as I would for pretty much any UNESCO site, religious or not.
That said, it will end up with no shortage of private and French-specific funding. I mean, I don't have the numbers in front of me, but it's freaking Notre Dame yo. I don't know if we need to throw our taxpayer dollars at it, with plenty of our own problems.