I agree with the diagnosis, but maybe not with the solution. If Wikimedia is getting "overfunding" and doesn't quite know what to so with it, there's probably plenty of good things to do. We could start a community process to decide it, because
as you say, reducing funding efforts or saving indefinitely for the future isn't likely to happen or even desirable, considering the alternatives.
Here are some ideas:
* Investing in clean energy sources for Wikimedia servers.
* Funding of external developers and libraries on which MediaWiki depends.
* Funding of open knowledge projects beyond Wikimedia, to not stray too far the original intentions of donors and volunteers.
* Funding of other non-knowledge altruistic projects (like buying land for a natural reserve). I'm sure the funding team could rethink and generalize the campaign to justify this use for future donations.