Extract does require a different strategy and yes it does hurt the almighty power of card advantage.
But it can give you power-advantage, even card-advantage.
Particularly if you are geared towards combatting plan A/B, e.g. if you are playing Leylines mainboard.
Playing 4 Extract + 4/5 Duress/Thoughtseize + a solid mainboard hate plan can quickly disrupt the Plan A or backup wincons of your opp and force him to follow a route set by you.
This strategic insight is invaluable, as you'll know what is important to disrupt (even if you have one card less to accomplish this), or when to trap ur opp.
Furthermore, the Extract-plan leads to dead cards and more resources spend on finding the remaining outs, which can be seen as a minor form of card-advantage.
But what I find most appealing about Extract is that it is blue and costs , and lately there has been a gap at that spot  , not that I see it as a replacement for BS, more like a blue 'Duress', in the right deck.

At the very least it should be boarded by painter to remove that pesky gaea's blessing... 

Although I am not a vintage player, it seems to me that, given the brokenness of the restricted cards and the extensive tutor-suite, the number of win-conditions has gotten pretty low. So to me, there is great power in countering your opp's win conditions pre-emptively. Yet, where extirpate is a bomb in legacy, it ain't so great in the restricted vintage meta.

So I am gonna root for Extract. : search opp lib for 1 card and remove from the game.
A first turn Extract to remove the Tinker/ a Tendrills etc. seems pretty solid to me! (particularly in combo with heavy grave-hate)
As a bonus you get to see what your opp is playing, and experienced players should be able to guestimate an opp's hand just from browsing his library. (you'll know when the recall or walk is missing..)

The same goes for Hide/Seek (as a Cunning Wish target?), though the manacost is not easily accommodated in vintage.

An ill-fated experiment in my view 

The difficulty in getting Dream Halls on-line, and the crap you need to run for when you do, seems to much to overcome.
Props to the one that cracks it 

I just like to add one crap card that might actually work in this deck:

Ideas Unbound:  : Draw three cards, discard three cards at end of turn (sorcery - freaking arcane )

The drawbacks are obvious, it is a bad card. It has less power than the alternatives mentioned, but it might make the deck a little more "reliable".
It can filter dead hands for 2 mana and is just powerfull enough to combo-off with dream halls in a single turn.
Not saying that it is great at these two tasks, but the possibility to do both (with and without dream halls) makes it worth considering...