Since I embark in metal free areas, I rely on goblinite, so the less valuable kinds have a high value to me, since I'd rather use a copper chainmail than leather armor while the iron slowly accumulates into a sufficient amount to equip another militia member with an item (passing though the stage to convert the iron into steel). Also, I like to give my dorfs underwear when possible, and the only source of that in any measurable volumes is neighbor donations (elven caravans seem to bring about 0-3).
A problem with cage dumping is that you need a lot of cages, and it's hard to avoid getting masterworks ones, which generate bad thoughts when destroyed. If prisoner recaging doesn't have any risk of escape, then you can cram all the prisoners into a single low quality cage, though.
I use a dual refuse pile system, with one for regular refuse and one for sapient refuse. The regular one accepts everything except dwarves, goblins, elves, humans, kobolds, trolls, troglodytes, gorlaks, ogres, and blind cave ogres for the corpse, body part, and tooth categories, while the sapient one accepts only those, plus the top level corpses category (since the refuse/*/dwarf ones don't work). As other (dead) sapients are encountered they are removed/added to the piles as I go. I just use quantum stockpiles for the refuse, although the sapient one dumps into a fairly deep hole to keep the old bodies out of sight. The sapient refuse disposal is indoors in a room with doors to keep the waiting bodies out of sight and the miasma locked in (although the room is large enough that miasma shouldn't reach out of the room anyway). I used to use magma, but the twisted satisfaction from goblin and elf bone armor and crossbows took over.