...A Magnet system wouldn't necessarily have to be realistic- goodness knows Minecraft isn't exactly known for realism. Rather, it could be combined with some of the existing vague sort of arcana system. Some ideas off the top of my head:
-Copper Pulsar block made with Lapiz and Copper, can be set to attract or push items towards or away, regardless of item type. This would be especially useful for farms, and wouldn't necessitate so much messing around with water. That being said, the range ought to be limited to prevent it from being too overpowered, or replacing traditional farming methods entirely. Redstone signals would switch polarization. ...Maybe it also works on mobs, to some extent?
-Copper Magnet block- this could be similar to something featured in Quark Oddities, in which the magnet block acts sort of like a piston, and is able to push or pull metal blocks within a certain range in the direction the magnet faces. This would be very helpful for elevators, doors, and all sorts of redstone machinery- and, if it only functioned on, say, Iron- such elevators would be proportionately expensive to build. (It would also be cool if this worked on minecarts!)
-Copper Armor is weaker than Iron, but has a unique benefit that could also give copper blocks a use- when wearing copper armor while adjacent to copper blocks, the player gets certain benefits. Copper boots normally aren't that great- but if you're running on copper, it gives you a decent speed boost. The Chestplate isn't the most durable, but it allows you to quickly ascend up a copper wall. This would be an interesting new way to encourage players to use copper within their base.
Alternatively, instead of having the normal durability mechanics, copper armor would lose durability in the same way copper weathers- semi randomly, and over a long period of time. This would be annoying, to be sure, but if copper is intended to be fairly common, it could make copper armor a sort of disposable early game set.