Just had an interesting game where I used this combination to overpower a couple of newbie opponents. I don't know whether this is objectively very effective, but it seems to work well.
The main idea is quite simple: scrying pool to draw a chain of actions, vault to discard them for money, scrying pool to draw them all over again. Repeat until you build up a vast amount of money, and buy lots of provinces in a turn. Vault and scrying pool by themselves are good cards, and scrying pool before the vault will help stop your opponents from drawing good cards from the vault discard and draw effect. You will also need at least one +action card to make use of this.
Secret chamber will also work, but vault is better because drawn by itself it's more useful, and it'll assist in drawing non-actions or, with a village, in hunting for those scrying pools.
Support cards:
Getting a source of +buy is essential to make use of large money rounds, and to acquire lots of scrying pools quickly. Best for this is worker's village, since with vault it'll also draw enough to avoid stalling, and it provides +action.
Cheap actions help, obviously, especially if they are non-terminals, to avoid dead hands without scrying pool in hand. Pawns or hamlets are nice. Alternatively an university or ironworks to build up on villages and so on.
Drawers and trashers make this really super powerful. Ideally you'd try to have as few non-actions in your hand as possible. Once you draw all your non-actions, you can then vault/scrying pool freely without risk, as long as you have the +actions to enable it. Buying treasures actively harms this combo.
It's hurt by curses, but mostly immune to card discarders.
