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Surely the nature of them being passive upgrades you just unlock them as you get the blueprints and they are all useful?
https://gyazo.com/2c3295703f5357a095c15ad0696fb8a0
They must have improved this since you wrote the guide, because twice I've noticed that even though I accidentally killed the last enemy of a wave just before triggering the cloud wave, and the wave bar did indeed increase normally while I dealt with the cloud wave, once I killed the last enemy of the cloud wave, the wave bar reset back to zero. So the technique you describe seems to be irrelevant now.
I'm assuming that you're talking about both the game plus the DLC, if you're only talking about the base game, then the next step is to buy and play the DLC since it takes place after the boss is defeated and continues the story/plot.