I think you may be interested in the
Triggered Recharge modifiers for Energy Reserve that Antoni worked up at my prompting.
These sound like they'd be useful for the "Someone casts nondamaging magic on me, I gain ER" case. Damaging magic would be DR with Absorbtion. Sucking it out of items would be trickier - I'm not sure Leech is actually valid here, but bending things around for houserules is of course possible.