I think the best bonus one could come up with for tier monthly subscriptions is ways to make the server better.
For example, an affiliate program where if I invite people who stay for one month, I get a little something.
Basically incentives to get people to join dogecraft. Because that's the one thing that would benefit both players and staff.
Another idea I had was a sub only dogecraft avatar + wallpaper, to share the love on the many "pic of your desktop" forum / reddit threads. This would be a nice way to start a conversation.
Also, for those out there that have a blog, a website, admin on forums or subreddit, or SMBs (small or medium businesses) owners, trade banners. For example, once my game will be live, I would be very happy to put a dogecraft banner on it, to make the server more widely known. I think ideas that make the server more popular are the best rewards, since, as I said, it would benefit everyone.
Take care everyone (btw I'm Chris)