For me, there are two completely separate arguments here:
1. Is Wikipedia currently run by people that I think have the right strategic direction and priorities?
2. Does Wikipedia greatly contribute to the world and could they contribute more?
On the first point I'm, um, politely, a little skeptical. Trying experiments is great, but mission bloat means that a lot of money is wasted on things that aren't at least presently making the world better.
On the second point I do not know how anyone could come to more of a resounding YES to. English Wikipedia is awesome, the Wikitionary project has helped me in multiple languages ranging from Russian, Greek, Chinese, and of course English. Would I personally prefer if they put more effort into getting Wikipedia English translated into other languages more thoroughly, especially the languages of poorer countries? Yes. Of course.
But the thing is, even if the ninety cents of a donation to Wikimedia is spent on what I personally consider to be less effective projects, the dime that is spent on things that I really agree with still buys WAY, WAY, WAY more impact than even a $20 donation anywhere else on education. So if you're going to donate $20 to your alma mater then I recommend either writing for Wikipedia or donating to it, because the impact is real.