Why I’m Only Planning Last Minute Summer Travel

Lucky, I've gotta second Dick Bupkiss here. I don't see any consideration in your post about the fact that while some countries are slowly reopening with varying degrees of precaution, those countries may exclude Americans from visiting in the early stages due to the way the U.S. has handled the COVID-19 situation relative to other countries. If I were deciding which countries' nationals could visit upon reopening, I'd also feel inclined to leave America off the list for right now.

Like other countries were quick to cut off travel from China when China was the COVID-19 hotspot, don't be surprised to see other countries treat the U.S. similarly for a while.

Here in Canada, We have restrictions for travelling domestically, unlike most of the US. It's not just the US-Canada border that's closed.

Domestically, there are lots of provinces that are off limits to out-of-province residents this summer. For two months I couldn't cross the river from Ontario to go to Quebec. My family had to scrap their plans to visit Prince Edward Island in June because tourists aren't allowed in.

And even in provinces that will be open to non-resident tourists, there will be restrictions.
Manitoba and Nova Scotia will require 14-day quarantine periods (like Hawaii), rendering week-long trips impossible. In British Columbia, only BC residents can reserve campsites in Provincial Parks this year.

So I'm mostly looking at trips within my own province.

You list four criteria for choosing places to which you might travel. I think you are missing the most important criteria:

That location's ability to manage a COVID19 outbreak - that your arrival might initiate.

Your other criteria tend to be more self-centered, me-me-me items: they provide benefits to YOU (ie, they help you reduce your chances of catching the virus). What's missing from your list is the crucial question of how well prepared is your destination to manage and contain the virus if a tourist - you - happens to bring it there and it gets loose in the wild? This is a serious issue and one that every tourist should be considering.

It's one thing to fly to, say, Denmark, and visit large cities, where the health care infrastructure is strong, a prosperous place where the government will be relatively transparent, will can and will take effective steps to contain an outbreak, and where you can feel OK about not bringing an undue risk to large numbers of vulnerable people there.

It's quite another thing to fly to someplace that has a fragile, already-saturated health care system, where the government is mostly concerned with pumping tourist money and less worried about poor people (who may have little or no access to quality health care even in the best of times) who might be devastated by a virus flare-up (ie, much of the developing world).

Don't be a tourist who shrugs off any sense of responsibility to residents of their vacation destination besides paying the bill.

In many (most?) cases, tourists just shrug and say "if the government will let me in, that's all I care about, I'll be on the first flight - it's their government, it's not my place to second guess that country's leadership." Just look at the leaders of Brazil, Tanzania, even the UK, and yes, our own USofA...you think just because the local Grand Poobah has decreed his hotels and restaurants sanitized and open for business, you think that's responsible to just follow whatever he says? (Imagine your country is lead by some corrupt goon who owns a bunch of hotels and doesn't give a damn about the people he steps on while stuffing his pockets...go ahead, that shouldn't be too hard to envision...).

Now, in your example, Ben, Iceland would appear to be a fairly responsible bet to make. Nordic country with a high standard of living, solid health care system, no large underclass without access to medical resources, reasonably transparent government, etc. But I would not blithely book an early trip to some developing world, tropical beach resort that does not tick all those boxes. As much as I long to go back to places in the developing world (I was dreaming of a trip to Mexico next winter), I'm going to give them some time.

Not because I can't book a flight there (I can do that right now). Not because the beautiful beach and reef or the resort I love isn't open (they are or will be soon). And not because I'm afraid of catching COVID19. I'm not going for a good long while because I know their health system is fragile, currently at (or over) capacity, and a virus flare-up could result in a disaster for those who live there. I'm choosing to be responsible and I'm not going because I don't want to contribute to a virus outbreak there that would devastate the locals (yes, even if those same locals invite me to come and spend money).

Your upcoming trip to Iceland (and it seems pretty obvious you have decided to go) may be OK and fairly responsible compared to many alternatives you could pick (although I still think nobody should just be traveling for leisure for a good while still - I've decided not to go anywhere for the rest of this year). But the criteria - is it responsible to go to this specific place, based on their ability to manage a virus flare-up - ought to be the first consideration on any responsible traveler's list. It shouldn't be an afterthought at best (most people won't think that far).

Try not to breathe on the flight.