I couldn't have said it better myself. From experience, I've ran both only noticed one thing. The aluminum's wear much faster than the steel's, mainly the water pump pulley. It wore very thin over time and caused me to ditch the whole set in exchange for steel's.
wear is the only issue i know of, i went with aluminum BBK's because of quality and looks.. they dont come with a PS pump pulley though FYI, i run a flaming river manual rack so its not a problem. I will always buy aluminum for no other reason than looks, steel work just as good but dont look nearly as nice, my BBK water pump pulley is in a box now because i had to buy a ribbed pulley to keep the belt from slipping on the smooth one(because i run from crank to water pump, to alternator then back to crank...) PM me for more info