[LeTharg]

The value also depends on the type of game. I'm playing in a game where you can only colonize planets of the same type and atmosphere as your home planet (methane ice in my case). That means 1 or 2 planets per system. So Natural Merchant might mean one more facility per planet.

There is also the benefit of getting cash flow earlier. If a space port takes 3 turns to build then Natural Merchant means that every production facility on the planet is done 3 turns earlier and yields 3 turns more stuff.

That said I've taken Natural Merchant twice and probably wouldn't take it again.