One critical element of Land Banking has been overlooked, Why are you purchasing and what do you want to do with the land?
Land banking is primarily a technique used by developers who plan to break the land up into house blocks once the area is approved for residential development. Yes it's a lot like looking into a chrystal ball and you have to weigh up the risks and you MUST know your exit strategies otherwise you are almost guaranteed to lose money. In some countries you will pay an annual land tax and this has to be calculated into your 'holding costs'.
Add the figures up carefully: Purchase price, entry costs legals etc, carry costs & taxes for the duration you are going to hold it, then if you are able to sub-divide, the sub-division costs, where I live (Australia) they are $100,000 per block created, then finally selling costs, then weigh this all up vs selling price, are you in profit or broke?!
This is what land banking is really all about, it is a business!