silicon carbide is harder than alox and is a blast media.

#1 reason not to re-use media is contaminants, you don't want to use rust and dirt as a blast media, so even though your media lasts a long time its full of crap and it needs to be changed often. Unless you have a cyclone for removing dirt/paint/rust i would just change the media on a regular basis.

brown aluminum oxide has silica in it as well so not a good plan in a enclosed shop with no outside venting