Generally considered by who? If you polled the general population, I think the position that rich lives are more important to save than poor lives would be highly unpopular. I certainly don't believe it. 

One factor is that rich people have more resources and ability to save themselves. If a millionaire and an impoverished person both need a ten thousand dollar treatment to live, obviously you should donate to the impoverished person!

VSL isn't directly comparable across countries. It's a measure of how much money people in a given country would be willing to spend to save their own lives. For example, if someone would be willing to pay up to $125,000 to reduce the chance of them dying by 1%, then their VSL is $12.5 million. These amounts are lower in poor countries simply because the people there have less money, and it has nothing to do with whether their lives are more or less valuable.

The value of a statistical life is determined by governments, right? Governments of rich countries value their own citizens more than they value the citizens of poor countries, which makes sense from their perspective, but it's not morally correct so you shouldn't accept their VSLs.

The point that it's better to save people with better lives than people with worse lives, all else equal, does make sense (at least from a utilitarian perspective). So you're right that [$ / lives saved] is not a perfect approach. I do think it's worth acknowledging this...!

But the right correction isn't to use VSLs. The way I'd put it is: a person's VSL--assuming it's been ideally calculated for each individual, putting aside issues about how governments estimate it in practice--is how many dollars they value as much as slightly lowering their chance of death. So the fact that VSLs differ across people mixes together two things: a rich person might have a higher VSL than a poor person (1) because the rich person values their life more, or (2) because the rich person values a dollar less. The first thing is right to correct for (from a utilitarian perspective), but as other commenters have noted, the second isn't.

My guess is that the second factor baked into the VSL is bigger in most real-world comparisons we might want to make, so that it's less of a mistake to just try to maximize [$ / lives saved] than to try to maximize [$ / (lives saved * VSL)].

I don't think lives of rich people should be more valuable than lives of poor people.

So, using [$ / lives saved] is the wrong approach. We should use [$ / (lives saved * VSL)] instead.

I strongly disagree with that.