Re: The question to ask to answer the question related to worth and future cost overruns
Well, the Spruce Goose actually flew...
Okay, not really - a short hop across Long Beach harbour, with a lot of goodwill. But IIRC a) Hughes paid for it and b) it was a huge leap forward in the construction of really big planes, for instance using hydraulics to move the control surfaces, that was a first among several others. All in all I'd call the Spruce Goose a 'successful failure' - didn't work as planned, but generated a lot of knowledge that was applied to other projects.