The tiers refer to total community progress. Higher tiers, individual rewards will increase (or maybe just the global, but I think probably individual levels will increase as well. We'll see), global reward will increase. I contributed 147T last night and I reached the 'top 70% contributor level'. If more people participate we can see what happens when we go up a tier, but people on the forums seem to be uninterested unless they see the numbers up front.
You can lead a CMDR to a new game mechanic, but you can't make them have fun.