I have never found the steam holes in the bottom plate of my iron have any effect on the ability of the iron to work. So every iron is a dry iron. I never put water in mine, steaming stretches fabric.
As for leaving it plugged in, do you at least turn it off? You cannot trust the auto off functions of an iron, just takes one earth quake, cat jumping on the ironing board, clumsy person walking past to knock that iron off (hence turning it on again). Turn it OFF! Unplugging has nothing to do with the life of an iron.
tim in san jose