@Turb007Part OneI already acknowledged that balance is relative to skill level in my last balance topic, Terran is strategically more difficult for lower skill levels, and Zerg has too few effective options to optimize with to gain advantage for higher skill levels.
In that sense I think it would be good to try out some new Zerg castable abilities that enable hard to execute but rewarding plays. Things quickly coming to mind are delayed explosions or restricting pathways. I like the idea for Large Spawner units to be such casters, it would give them greater importance and variation. It would then also be possible to make an effect last until the caster is dead, allowing Terrans to escape perhaps difficult situations by sniping them, a channeling time required before a cast could create similar situations. Let me know if you come up with different ability types that could be good.
I have to think a bit more about T1 Spawners getting a nerf to their capacity upgrades.
Part TwoMaking a structure increase in cost for subsequent constructions isn't that straight forward in the editor. In the past I've tried getting this to work, but I there were complications. Perhaps now I could get it to work. It was also of interest to make individual spawner types increase with amount such that it promotes creating different units and/or getting the next tier. However, I fail to see the motivation for an internal bank for only spawners. It sounds to me like it's simply limiting choice as to where to use the refund.
Energy for Large Spawners also acts to limit them. Without it, it would be quite easy to rebuild them and thus lowering the skill cap on that aspect. For a Terran it might also become less meaningful when they manage to destroy one. Perhaps a longer construction time combined with increased cost could address the issue, but I'm not entirely sold on the idea of removing the energy requirement.
Side note:I'm currently still working on a patch which takes me quite a while to figure out how to accomplish certain Siege Tank abilities. Also making everything comply with the vision restriction to the Zerg base took a while. However it's getting near completion so then I can move on.