I'll qualify my comments that the terms I used are all somewhat or completely non-empirical, including the "expensive" aspect.
Expensive: Estimating the total cost of US involvement in Mideast conflicts since 9/11 comes to at least as much as your $4T WWII estimate.
This site claims $5.9T for all Mideast military involvement, far higher than your $1T guess. I think both your estimate for WWII and the one I found for Mideast conflicts are both high, but the Mideast costs are still higher than WWII.
You'd have to figure out a metric for "most destructive", but I'd say flattening Dresden, Tokyo, Hiroshima, Nagasaki wins hands down on their own against the Iraq war in human lives and destruction of roads, bridges, hospitals, apartment buildings, and on and on.
I'm inclined to lean your way on this point for lost lives, but our Mideast engagements had both massive direct costs in deaths, population displacement, and ongoing resulting deaths and displacements that go beyond just lost lives. I can't give a measurement for that.
Gulf of Tonkin was at the time understood to be really sketchy, while Hussein's Iraq clearly was launching missiles. Similarly, the Maine was a total cockup pushed by Hearst, of very dubious reality. It would be like if Bush had launched the Iraq war because Fox News kept publishing crap about Hussein and Iraq. And geopolitically? The Monroe doctrine is a lot more suspect than the idea of establishing a heavy boot in the Middle East. Spain wasn't even a real enemy, we just wanted to scoop up Cuba for our own interests. Misguided? I'd be hard pressed to find out how Iraq war would beat out either of them.
I think you and I would be in agreement that all of the major military conflicts (except WWII) the US has fought were avoidable. I'll argue that the second Iraq War eclipses the others as being misguided, since we launched it under the worst possible phony excuses. Every single claim that was used to justify it initially was false, and in combination with the still ongoing war in Afghanistan, had virtually no change of achieving the advertised goals. I'll never understand how our "leaders" at the time escaped accountability and punishment. We've "litigated" the casus belli for these wars often enough on Ornery already, so I'll leave it at that. FWIW, I also thought the first Gulf War was a huge mistake that led to horrific and unanticipated consequences. That hasn't been given nearly as much attention here, but it's probably not worth spending much time on it at this point.
Disastrous? That's the most ambiguous of the four, and overlaps with the others to varying degrees.
I'll comment on it even so. There's no question that WWII cost the most lives of any conflict in the time period we're talking about, if we ignore Asian conflicts and disasters (such as the preventable Chinese famine that killed 10's of millions of people) the US didn't directly engage in. The US foreign policy in the Mideast has been a colossal disaster, to put it mildly, for the 100 years since we carved up the region after WWI. Everything from that time through the establishment of the Israeli state, our wandering support for Iran vs. Iraq and vice versa, all have served selfish US interests in acquiring steady and low-cost access to the region's oil. There's no other consistency to our national policy guiding which autocratic or despotic leaders we support or oppose (and depose).
Ignoring the major Iran/Iraq war of the 1980's, that led to the first Gulf War, which we fought solely to "protect" Kuwaiti oil supplies. The aftermath of that war plunged Iraq into a decade of horrific human rights losses. It's estimated that 100's of thousands died in Iraq died during the interregnum as a result of leaving Hussein in power.
The death and displacement totals from the second Iraq War are almost certainly much higher, with estimates I've seen ranging from 200,000 to almost 1,000,000 death and many millions displaced or suffering long-term injuries. That doesn't include Afghanistan, which to some extent "suffers in silence" due to poorer war reporting coming out of the country.
I'll stop here with the general comment that you can rank wars over the past century or so to make some appear more evil than others and the arguments to fight them more mendacious for some than for others, but in my mind nothing compares to the wholesale multigenerational rape and pillaging of the Mideast.
[I spent too much time on this already, so I won't review it to edit mistakes...]