One important note is that expanding a base’s area with a permit is not permanent. You can later remove buildings and refund the permit. So there’s no reason to hold out on expanding a base if you can use the extra area right now, vs making better use of it in a month or two. Obviously that does not apply once you start getting base upgrades that cost hundreds of thousands of coupons to do.
That doesn’t mean that I think the doubling cost of each upgrade is reasonable though.