westhawk, what an erudite post. I think that you've covered the past completely.
However, after my education last night I have been chatting with an Engineer mate (me Naval Architect, but much the same really).
My take was to use waste heat from the propulsion engines to heat the Helium to gain height, and then use power to cool and compress the Helium, to avoid dumping it. Which is not clever in a Helium poor world. Off the top of my head, I'd thought Hydrogen, lot of it about and could be relatively safely used.
His thought was vacuum. Nothing on Earth weighs less than that. Obviously not possible to get a perfect one, but it's possible to get pretty close. Not that costly to build a light containment?
Thoughts all?