Scout with the right victory cards (great hall, nobels) can create very powerful engines.
Uh...no. It really doesn't. It arguably can do something useful in cases like those, but at the end of the day, the two problems with Scout are that it costs $4, so there were almost certainly other things you could have bought instead, and that even for its intended use (sweeping green cards into your hand) it doesn't really do all that good a job of it until you have a lot of VP cards.
So imagine playing on a board where you had both Scout and Great Hall. Gotta be engine time!! Or not. If you buy Scout/Great Hall on 4/3, you will usually now have 3 Estates, 1 Great Hall, 1 Scout, and 7 Copper. That's 12 cards, of which 4 are green. We reshuffle, and you have Power Card Scout in hand!! So how many green cards will you be able to snatch from the top of your deck when you slam that bad boy on the table? Well, you have on average about 4/3 green cards in your hand to start leaving 8/3 green cards out of 7 left in your deck. So the probability that any one card is green is 8/21, so the number of greenies you pick up in your top 4 is...about 32/21, or 1.5. Had you just played a cantrip you would have picked up 8/21 green cards, so Scout here gained you one green card in your hand, where you then, well, uh..what exactly? I will be charitable, and allow that you just picked up your Mighty Great Hall. So I plonk that sucker down and pick up...a Copper. Now you have a hand consisting of 4/3 of a green card, $11/3. I will even let you round it up to $4 and build the engine from there. Good luck with that. Now, to be fair, maybe you meant something different. Like you had an engine built out of Nobles, or some clever use of Throne Room and Great Hall and other stuff, and Scout will improve that in some way. I'm still not seeing it, since in the Nobles case you probably were better off with a terminal Silver (to help buy more Nobles, say) and in the TR-Great Hall case either cards that really do draw or else payload. Scout is not payload.
Alternative scenario: On your board above, I do something mega boring like buy Silver/Silver (I always can). Now I have a money density of $11/12 cards = .92. I reshuffle, pick up my hand, and have a 50% shot or so at hitting $5 on Turn 3. $5 cards are really good cards, on average. And so forth.