Screw this say yes thing. There is almost nothing worse than the "Harvester" player.
Hey, I killed a monster? Can I harvest its organs and turn them into poison? There's poisonous spikes at the bottom of the pit? Well, I guess I gotta climb down there and get the poison off... Fungus? Is it poisonous fungus? Can I harvest this poisonous gas in a bottle? That scummy water... If I put it on my weapon, would it be poisonous?
I personally love these types of players. I find it enjoyable to let them use their creativity a little bit and then throw a complication at them. Sure, that was a poison fungus, but after production of the poison you find that it is contact poison. I much prefer the "say yes" + complication than a say "no". Match creativity with creativity. Saying yes does not mean that they have the last word.