After reading Tooze's, I believe part of the reason why late-war Nazi weapon development programs were flashy was for internal propaganda. Kinda like ego-booster, but for the masses, not the generals.
The general picture in 1943 was bleak. Supplies and manpower were running out. People at the top can see things teetering (some would argue it was going down already). But the German people were still laboring diligently in the farms and factories. The conquered population were still being squeezed dry for their resources and labor. So Nazi Germany needed to make their people and the conquered people think that they would still win the war. Thus the flashy projects, messaging of numbers, and careful selection of news. It's not like they can admit that they were losing. Above all, morale of the populace must be kept high. There were to be no riots and no strikes like back in WWI. And the conquered population must be kept cowed.
It didn't work as well as they wanted, but Nazi Germany really wanted to make sure that the domestic front was under their control. The Nazis believed that Germany lost WWI not because they lost to any foreign powers, but because Germany was sabotaged from the inside. So they wanted to make sure that this time it wouldn't happen that way. Hence the need to portray things as a-okay.
Parallels can be drawn with the Iran's bombastic pronouncements of new weapons and with North Korea's announcements of new projects.