I think it's safe to say, depending on one's situation, but:
blown headgasket:
if engine has less than 150K, job about $2-3K, could be worth it.
if engine has more than 150K, job about $2-3K, get another engine.
STILL, $2-3 is still cheaper than getting another SUV. Again, lots of other factors.
If mine were to "go" (I'm at 111K), I'd get the job done. I expect this rig to last at least to 250K miles.
Are low mileage used engines readily available for ~$1,500? I just don't know anything about sourcing one of these. I have no way of doing an engine swap by myself, and I imagine the labor/additional costs involved would be at least another $1,000. With these things failing at ~150k miles, I would be hesitant to spend $2,500 on an engine with anything over 50k miles. You can spend $2,500 on a used engine with 100k miles and then have a gasket fail at 125k like some people here. If the gasket replacement is done properly, I would imagine you should be able to get another 75k-100k miles out of it, provided its in good shape and has been well maintained. Or am I being delusional?