I am the owner of a server and I can say that you make no money whatsoever, all the money in donations we receive goes to keeping the server online, and if we make profit, it is kept for the next month's server bills in-case donations don't quite cover it.
Working as staff or owning a server is completely voluntary, it's like owning a YouTube channel, most do it because it brings pride to have made something people enjoy.
I would say it is worth donating, especially on servers you enjoy, as donations are what keep it afloat. Most of the times I have donated to servers wasn't for the perks, but more for the title it gives you, you feel proud to have supported a server you enjoy.
