For instance, we can compare Harvest to Navigator. Navigator always makes 2, Harvest makes 1-4 (usually 2-4, probably most often 3 followed by 4 followed by 2, 3 being about average). Navigator looks at one more card than Harvest. Navigator lets you keep the cards on top of your deck if you want. Navigator lets you re-order the cards if you keep them. Navigator costs less. Harvest can be sapped at no money if you draw all of your deck, whereas Navigator can't. So almost the only thing for Harvest here is that it tends to make more money. Okay, that is one of the most significant factors here, obviously. But I also think the cost is really big, as Harvest has a lot more to compete with at $5 than Navigator does at $4. So it seems to me that Navigator is pretty clearly better than Harvest.
Little analyses like ^that^ are some of my favorite things to do.
Harvest and navigator is an interesting comparison.
Harvest gives $3, often $4 (and $4 is a lot of money). It discard cards which is good unless you don't want to trigger a reshuffle. The discarding effect can be useful in decks with sifters, or things like courtyard, mandarin or opponen'ts ghost ship. So yeah, in this case the discarding effect is a little bit like navigator. But often, navigator is simply a waste of time because it simply doesn't provides enought money, and can't really help to get a province. It compares to silver which is cheaper. Harvest compares to gold, which is more expensive. Harvest gives like $3,5 and with 4 other cards in hand (a good average money density) you are likely to have at least $8.
I see Harvest as a money provider, and while there are a lot of good $5 for drawing or attacking, there are not so many money-providers. And when you need one, Harvest is great at this task, and IMO generally better than say, Royal Seal, Merchant Ship, Mandarin, Stash...