E boost is actually a great skill, good for when lixes are in a shortage, and to avoid reliance on sigils(because they hurt your dps by having to stop casting to sigil tick, unless you are a pure ice mage).To add to what should be considered quality of life.
Reduce the drop rate of e shield, e boost, e harvest. And all other neglected skills to be as rare as apostate spawns.
There's a reason the skills aren't used. You can't make them desirable just dilutes the boss drop table.
I do like that you suggested a drop rate reduction instead of removal, because people ruined decent ideas in the past with that(I would have liked to see how a warrior tank using a godly bandage wounds mordy brace would have done in 2013, but people were stuck thinking it was automatically bad). I don't think changing the rates is the way to go though.