If your putting population structuers up as well you should think about the astrobiology ward.

I'm all for trying new and innovative ideas, especially when it comes to planet construction, but I gotta say I think this would be a poor road to follow. I think VL planets just lack the space to properly defend. Even when I only had roughly 10k attack, I would routinely succeed at taking planets with 30k+ invasion defense. So that would be the minimum I would feel comfortable having on a planet like one you're talking about. Or 15k cloak. Either way, you'd be sacrificing a significant amount of space to protection. Secondly, maxed out mining toxics are relatively easy to make. Maxed arti toxics, not so easy. There is a significant investment in doing that. Either by Taltherian uplifts or terraformers. It's much easier, and cost effective, to max out a VL Terra or Desert because they commonly have a higher natural artifact bonus. I personally don't bother invading mining planets because of cost, they're cheaper for me to build via toxic purifiers, but I do look at them when I scan one. Just to see if there are any interesting artifacts in place, so if I scanned an arti toxic I'm taking it and/or serving it up for our legion to take. Chances are very good that we're going to get it. Toxics I only put enough defense on my own to keep newbs from getting them. High ranks rarely bother taking mining planets, they are too easy to replace, and extra defense takes away from production. I dare say the effort involved in making one 15x arti Toxic would be better spent making two Terra/Desert planets plus a maxed mining Toxic. Most likely an equal (or only slightly higher) energy/resource investment in building those 3 planets will net you a much higher hourly payout.