Reducing the costs is absurd due to the possibility of a very early OC. That can make quite some difference on maps with a lot of tree reclaim since that's how you'll get the energy. e.g. if you can make 3 OCs more than your opponent, that's 900 additional dmg to his ACU (on Seton's, for example).
There is no need for energy storages except OC and very lategame anyway. Adjacency on shields etc. won't do the trick either since noone is like "I can save energy with adjacency", they just build a new PG instead. The total outcome is basically non existent when you compare it to regular PGs and the main problem why noone spams storages is the mass cost. But then again, if we reduce the costs go to the first paragraph.