IMO, do not make blaze rods a common trade. The server should keep things 'harder' and more tedious then everybody having access to everything 24-7. Make people go find a blaze spawner in the nether. Make them get it through trading with others.
*The more player interaction, the better the server develops.*
Ghast tears are a pain in the butt to get, however. IMO keep the good stuff out of the auto trade zones. Let the economy rest in the players' hands.