Currently, server that are below your skill level are invisible to players of any tier. With regards to T4 players especially, this limits the amount of truly skills matched play time you can have, for most modes other than CA.
I would like to suggest an update that would allow players to see and join servers 1 tier below their own, but perhaps forcing a handicap so as not to skew the skill level of the server. (I think 75 would be a good start.)
Perhaps making it a premium-only option would give players more incentive to subscribe.
Right now, it almost feels like being punished for taking the time to get good at QuakeLive - aside from spawned, unrestricted servers, I rarely see more than 3-4 populated servers on any given day.