I expect WBs will still be useful even with per-planet energy, because sometimes AI forces are just too strong and are likely to cause a lot of collateral damage on whatever planet they target most. The point of the WB is that you care not-a-bit about the collateral damage on it, whereas on other defended planets you kinda want to keep the collateral damage to a minimum usually, heh.
I think we'll see a lot more defense-in-depth, which I'm really excited about. And that may reduce the frequency of WBs and certain other tactics. But I think they're still something that is likely to be inevitable when there's a lot of "splash damage" from an AI wave that you want to have make a mess somewhere you don't care about.
