One of my friends and I were talking the other night about the state of the game. We came to the conclussion that Tier VIII and X are the ones that are really worth that much for playing these days for our small clan of casuals that rarely have premium time active.
Basically Tier VIII Premiums to farm credits in order to feed youlr Tier X Bond farming when it comes to Randoms. Tiers V-VII can be used to farm credits at a slower speed if you don't have a Premium VIII to use.
Tier VIIIs also come into play for Frontline mode.
Tier Xs then have Brawl mode, or Ranked for solo or 2/3 man platoons to particpate.
Clan Wars/Global Map, Tournaments, and Stronghold battles are not really viable for us when re rarely have more than 2 or 3 players in the clan on at a time. Add the Blueprint fragments and Free XP system reducing the need to buy and grind out the other tiers to get the VIII and X tanks makes the other tiers pointless for those like us. Saving credits on discounts and skipping tiers means less grinding for credits just to afford to buy and play the Xs to get our bonds.