Most of the gravestones I have encountered have been in the catacombs which are plenty difficult to explore, and the loot is fairly balanced. I ended up with a TON of bones (something like 20 stacks), and a bit of other random things (leather armor stone swords, clay, redstone, occasionally gold) from the entire catacombs worth of gravestones, so specifically what are you talking about?
I haven't encountered a catacomb in magic farm yet, but I did encounter one in my personal modlist, which generated alot of graves at the surface of the catacomb which you could all loot.
those had quite alot of iron/gold/diamond loot in them.
but an item to set your spawn does seem more fitted for MagicFarm, as it forces you to make this item first before you can really move away from your spawn, unless you're willing to spend alot of saturation travelling back and forth. perhaps this item could have a durability to it, so it'll break if you use it too often
and having certain effects when sleeping would also be nice. for example if you sleep too early, you'll wake up being very lazy, giving you a minute or 2 slowness effect when waking up and using up alot of saturation. you could drink a cup of coffee or something similar to get rid of the slowness effect and refill your saturation. if you sleep too late you'll wake up with a headache, giving you an effect like poison and taking up more saturation. eating a good breakfast would also get rid of this effect. but if you sleep at exactly the right time at night, with a span of like 10-15 seconds, you'll wake up with no saturation loss, and you'll actually get a very short regeneration effect.
perhaps certain conditions could also effect your sleeping and effects. like if you try to sleep during rain, you'll sleep alot better and lose less saturation. but if you try to sleep during a storm, you'll lose more hunger. and if you try to sleep with too many mobs nearby, you'll lose alot of saturation and get a slowness effect when waking up because you were too scared to sleep...