Are you asking about Return On Investment? If so, I don't know how that could be the case to get a positive ROI. Each B-52 cost millions of dollars (Wikipedia gives a cost of over $9 million per for 1962), and a loss of 31 of those bombers during the war. That's over a quarter of a billion dollars lost, which doesn't take into account the human costs (or logistics, or weaponry costs, etc).

If I am off base regarding your question, could you clarify what you meant?

I don't think the question makes sense as written. What would a return on investment look like, in this context? You get returns on investment when you buy productive assets, ie farmland, factories, businesses, human capital. Here you have money in, money out, so you can calculate an ROI. When you kill people and break things, you get, at most, political or foreign-policy objectives accomplished. The inputs are money and lives, the outputs are peace treaties. Even if the Vietnam war had ended in a peace that the US liked, how could you measure that against the money put in? (Much less the lives.) An ROI is a ratio; you can't divide "good peace" by "X million dollars" and expect to make any sense.

All that aside, since the US lost the war, the answer has got to be "no"; when you spend blood and treasure and get back nothing you wanted, that's pure waste quite apart from any philosophical difficulty. The US wasn't there to kill Vietnamese (which the carpet bombings assuredly did accomplish), it was there to prevent the reunification of the country under a Communist regime. Since it failed at that, the return was zero.