Actually, it isn't. The money is in the first to logs with Vista on each planet or moon you land on with a first footfall, so doesn't matter how many duplicates you get after you've already got the Codex's, each duplicate you find afterwards will get you that hefty first to log Vista bonus for every duplicate plant. That's why, in this system I found with 70 bios, even though I've already got some Codex's on this first moon, I'll still go after any duplicates on all the other moons.
(Providing I can stand the pace, that is.

)
The Conchas here are only to be found in a tiny bit of blue and I had to go arou nd the other side of this moon to find them. I wonder how much salad there is in all those systems up there in the sky and how much it's all worth?