I would have to admit the smelter wouldn't be my first choice about going for plant reactions, I would use the wood furnace for converting wood thread to wood *it was designed to be something similar to charcoal*
Also the value used for a year is wrong, a season lasts 1008 *something forget what exactly an* so a year would be 4032 *4 seasons of course*
Also the approach is good and logical, especially when you consider the tower-cap thing is like a crop variety of everyone's favourtie underground tree, which is simply being cut up and processed, would say though what you are getting logs without the need to cut trees down or go outside, isnt really compensated in this plant and reaction, while it takes a year to grow, with proper farm management you would get a continuous supply of wood at a minimal labour cost, also you always know every plant you grow will end up as a log and 2 seeds
My wood crop by comparison if you arent careful will be eaten or brewed, though admittedly this is simply remedied by turning them off from being brewed in the kitchen menu, which though would still leave them allowable to be eaten, which in a large fort if your primary source of wood is the wood crop then you could be in for a nasty shock, which is why I put a 100% success rate on the reaction and all the other reactions at that, this is more of a blessing towards smaller forts than large ones, though in any situation proper management would mean it would work out ok anyway =P Admittedly my crop takes half a season to grow though which would be the same as a plump helmet, maybe a balance issue i should change, but I set my iron crop to a season and on a linear value to grow time scale and by my standard wood is not as valuable as iron, though arguably wood is one of the most valuable resources there is =/