Okay, look. No matter how specialized your deck is, when MORE than half your hand is needed to be of a certain type to net a benefit, the card should be cheaper than the cost of the half-hand benefit. As Moon castle, or Prairie.
Do you understand? No one would want to play this as is. YOU wouldn't want to play it. Don't use more than the middle case scenario as an example, you work with five cards in your first one. Chances are, even in a dedicated deck, you won't have as many. Far Sight cards are not Brigands. They don't fill up your hand even when you take most of them. They cost a large variety of resources(thus you don't just run out of one and are unable to play the rest), and you need to play them while the opponent's hand is visible to gain the benefit. A Far Sight played is followed by another Far Sight played as fast as you can before the opponent denies you the chance. Many times, you won't have 3 in your hand, and that's good. That's what you wanted.
The closest to the concept now is Reliquary, Reliquary breaks even at 4, and even then it's just mediocre. Banish saves it, really.
Which is an aside to the fact your hand will NOT be full of Far Sights unless you stuff your deck chock full of Far Sights. Not in a dedicated deck, not ever. You've already paid for the cost in how much Far Sights had you stuff into the deck to make the card work.
To talk of 8 Far Sights in your hand is the same as to talk of Dwarven wall at 14 Facilities. You're farther ahead of yourself than any card can foresee. You had to, on your own volition, work for the eight keyword cards in your hand through summons, and smart play. You've already spent resources to achieve the feat. Cards. TURNS.
Just to break even on a card which wouldn't be worth your time otherwise? You're wasting precious turns, resources and time on a loser's game. Play a GOOD card. Play it NOW. Not a BAD card you needed to spend multiple to turns to make good LATER.
Dwarven wall is good at the basic assumption. 9 wall plus runic for 7 bricks is good. As a common card. All knowing eye doesn't pay for itself at four Far Sights in the hand, All knowing eye included. The reason Dwarven wall and Reliquary is played is the reason All knowing eye would NOT be. You need to fiddle around with all three, but the former two give you your time's worth back, and they tend to be good even when you do nothing. All knowing eye doesn't and is not.
We clear?