I'm pretty sure the badge is for donating anything at all. Otherwise it wouldn't be fair, people who can't afford 5 coins at once would feel like "hey, I donated as much as I could, I want a thank-you badge as well D:"
You donated so you get a badge, but the amount you donated is gratified with the certain perks attached. So I guess the badge is for everyone
At least that's what I think, Firn can always correct me
At first I was a bit scared about what people's reactions would be and I was afraid this would divide the community in two groups. But so far it's fine and if it stays that way it might even help with small donations

People see shiny, people want shiny XD
I cross my heart for that.
