I think paying for writing would be a giant mistake. There's a big psychological difference between working for intrinsic rewards and extrinsic rewards; the former gets you much better work. There's also a huge problem with paying some people and not others; my guess is a lot of volunteers would quit immediately if other people were getting paid for similar work.
I'm not quite clear on where the Wikipedia donation money goes though. But if they have a significant amount left over, they could use it on something worthwhile like fact checking.