Farmlanding Estate into Caravan early doesn't seem super-appealing to me. It's a lot like just buying a Caravan, since you end up with the same deck composition in the short term. Long-term, isn't it basically just a $2 down-payment on a future Province turn? ie, you can buy a Province for only $6 if you have your Farmland in hand. I think I'd rather just have the Gold, which is worth $3 every time I draw it, than a Caravan and an eventual $2 discount.
Later on, when you want to green anyway, it's a great layaway plan if you can't afford $8 because the Militia keep hitting you.