Re: [Spaceships] Making a setting work...
 

I wouldn't say he's Poor, but he's certainly not Wealthy. However, I would submit that Mal's ship is GM fiat in action; Joss Whedon is not the type to do detailed economic analysis, and Mal has the ship because Mal having the ship makes the plot work.

Re: [Spaceships] Making a setting work...
 

I have to say, I would generally consider any owner of a singularly large and valuable property (like a starship) to have some increased level of wealth. While they possess the starship they enjoy a higher status as a starship captain, and the continued opportunity for a high level of income through its operation - whether they choose to use it as such or not. Isn't that what Wealth provides? I would generally allow multiple levels of debt to represent the ship's expenses, and might require a couple on principle!

Not necessarily - Wealth gives your social status for free, it does not guarantee anything else. There are plenty of wealthy people in fiction and reality who are reclusive, unpopular, and boorish. Mal enjoys the status of a starship captain - uniquely tied to his wealth.

Wealth doesn't require that you spend it, or that you spend it on appearances - Mal spends his considerable income on the ship's expenses and paying the rest of his crew, many of whom he does not technically need.

Re: [Spaceships] Making a setting work...
 

But he couldn't give up captaining and get a cozy Multimillionaire's job, and just live on the Serenity. He can't do big-time Multimillionaire business — he smuggles cattle. Mal's status as a ship captain never seemed to be very high — almost everyone looked down on him. Inara was the one with Status, not Mal. Inara's job on Serenity was to make the ship respectable.

Re: [Spaceships] Making a setting work...
 

Wealth provides more than that, or is meant to. Credit, for instance. Mal's credit rating is approximately 'Guard, throw this scoundrel out of my bank!'

It also provides less than that (though it's not meant to) by failing to factor in to job-hunts...
The Advantage Wealth is a poorly documented thing, but it seems firmly established that it's intended to involve being tied into a social network.

This doesn't preclude being reclusive, unpopular, or boorish! Fiction and life both indicate that the rich don't need to be nice to be cut into the whole upper-crust deal. If you're entirely cut off from society and live alone in a mansion with gold bars in the basement, you're probably not Wealthy. If you're seldom seen to leave your penthouse apartment and seldom talk to anyone other than your stockbroker and your personal assistant, you may still be a Multimillionaire 1.

Mal does enjoy some status (and Status) as a spaceship captain (not actually a starship...the 'Verse is weird). But I'd say it's Status 0 or maybe 1, not what you'd have if you had Wealth to cover a multi-million dollar spacecraft.

(I'd say most people on the outer worlds are Poor or Struggling and have negative status.)
It is interesting to note that the only crew members who seem to serve an essential purpose are Wash and Kaylee. None of the others seem to have any technical skills relating to spacecraft operations at all. Mal and Zoe can stand watches, but if they've got any applicable abilities other than reliability and leadership it doesn't seem to come up...

Though nearly half the effective crew members are (or at least originally were) passengers. They might not be on payroll.