Of note is a tiny piece of counter-intuitive math that I like to bring up to newish players. It applies to all draw-2 cards, not just Moat.
A draw-3 action isn't 50% more powerful than draw-2. It's twice as powerful. New players see it as "almost as good."
Since each card you buy also adds a card to your deck, when you're engine-building, buying a draw+3 effectively shrinks your deck by two cards. buying a draw+2 shrinks your deck by one card. It's half as good. It's like the difference in trashing power between Steward and Trade Route. (Notably, non-terminal draw+2s are effective because you buy the same number of cards for the same amount of drawing power as a village/draw+3, with the added benefit of more reliability.)
When a player sees that, with no trashing, it would take 5 copies of Village/Smithy to draw deck, but all 10 copies of Village/Moat to draw deck, that should hammer home the point.
Speaking of hammering home points, something else I see with alarming regularity is players underestimating the importance of +card in general. They buy too many terminals, or too much treasure, or too many +action cards that don't draw at all. Drawing even one card is a BIG DEAL. Seriously. It's what makes those yellow cards poison. It's why Baker is $5 and Candlestick Maker is $2 (and it even needed a +buy bump to be relevant!) Also, Pathfinding says Hi.