CubeBuilders Is the most amazing server. That is why it deserves only the best. The best minigame (in my opinion) is SkyWars. Which is something the server does not have. It could replace the survival games which has been discontinued and as it is such a popular game, I believe the server will see more players join.
My second suggestion is that the Mob Arena is fixed. I say this because it awards you diamonds and emeralds for playing well, however you cannot take them putside mob arena and you cannot exchange them for cubetokens.
I also think that the cubetoken store on factions should sell obsidian. This would be great because although it could be sold for an expensive price. It means players will not have to get a diamond pickaxe to make their base more secure, therefore less people will rage quit because their base was raided on their first day.
These have been just some suggestions. More suggestions coming soon!