I disagree on saying the improved DAE would be only on par with the V1 Fusion Plants. While they would have the same average Energy per die efficiency (4 EpD), the Energy per R efficiency of the improved DAE would be twice that of the V1 Fusion plants (0.4 EpR for Improved DAE and 0.2 EpR for V1 Fusion). Now, will they be more die effective then V2 Fusion, probably not. But it will almost certainly be more effective per R, and won't cost any exotic resources, which may or may not be the case for V2 Fusion.
While the Plan as it is doesn't require much additional Energy given our current surplus, that is assuming we don't produce any non plan energy consumers, which is a poor assumption at best. We will need more Energy, and improved DAE gives us a ready source of issue free Energy at a solid efficiency. And as has been mentioned we will need to execute the off-lining of the current V1 Fusion and refitting it for V2, and that is probably going to be the main source thrust of Fusion in the future, keeping the old Fusion plants from collapsing our economy around us.