Short and sweet, remove the afk timer.
Donators already have an advantage having donator perks that allow them to have access to kits, flying, better mines, hopper limit extensions etc. Unranked players literally stand no chance against a ranked player who can afk farms 24/7.
I myself am a ranked player and have acrued a fair amount of wealth ingame so I can just buy my alts ranks and this in theory wont affect me and this will be true for a fair few others too but then the gap between non ranked and ranked players will grow even larger, It wont make more players by ranks, Its going to cause them to quit, Whats the point in trying if you have not a hope in hell of succeeding.
I'm sure there will be many others that agree with what I have said.