Ah, right, minimum cost. I'd forgotten that the plot costs typically started off high and slowly dropped, not the other way around. X)

But yes, I can't see the benefit of relinquishing the old plot first for the gil; main thing you're going to use that on is another house anyway. It's safer to just save up as much gil as you can and take the relocation cost as a perk rather than risk losing your old plot, miss out on the new one, and end up with a huge surplus of gil and no where to spend it.