I feel your pain, I do think once you get past 6 players your just adding on dead weight as opposed to enhancing the game.
If this truly feels like a problem to you, then I suggest the following:
1) Stop the game your playing. Start over, start fresh with a new campaign.
2) Pick 6 players. Either pick randomly for true fairness, or have each person submit a character concept. The 6 you feel are the most interesting and the ones that will work the best together remain, the rest are out.
It always sucks have to knock out players, but if your game is suffering from the weight, better to have one shock of pain then feeling that pain week in and week out as your game slowly suffers.