After the first reshuffle you will probably have 12 cards and the maximum value of those cards is $12, more probably $9-10. So on the second run through your deck every card has a rounded average value of $1, and over the extended series the equivalent of a $3p hand on turn 3 is a $4 hand.
The problem with that is that averages go out the window when you draw an actual hand. Because, let's say you open Silver/Silver, and you get them both, plus three Coppers, on Turn 3. You can't say that that's a $5 hand, because that's roughly your average card value at that point. It's a $7 hand, and the reason you have to look at it that way is because it means Turn 4 is really going to suck, average card value notwithstanding.
For any hand with a Potion card in it, you have to consider that that Potion could have been a Silver. Not $1, because you wouldn't have bought a Copper with that money but Silver. Whenever you've got a $3P hand, you could have had $5 instead. If you can buy a Golem, you could have bought a Gold. Etc. Thinking about it that way really helps in weighing whether or not the Potion-cost cards are worth shooting for.