You see, if I were you I would come up with my own. I'm too fucking dumb to do something like that and you're quite fucking smart when it comes to shit like that. So, to be honest, if it doesn't cost you anything to make your own, you can drop all that crap and keep the money for other shit.
You said it yourself you're using so little of their shit services so I don't know what's the hold up when it comes to coding your own thing. The way I see things, you're saving yourself money & you'll have more uniqueness on the server which will be greatly appreciated by all players that play on this server and that, my friend, includes this Croatian noob in Minecraft. :)
Better invest into better gear for the server, unless you got the best of the best, ya know, top notch shit.
I would always invest into shit that gives me more benefits. Your every penny you earned from donations is worth to invest into better stuff because that motherfucker is literally overpricing the living shit out of services you most likely don't or will never use.
It's up to you though, I never touched anything regarding server AI(which I still got no fucking clue what's that) so I can't say anything regarding that. :)