The Astros are trying to turn over their roster. So while their payroll isn't very high, I recently heard an interview with Jeff Luhnow, their GM, and they're using their profits to allocate to draft picks and the international transfer market. So they're spending money on players, they're just not here yet.
I'm with cardsfan, I don't see a problem yet. A lot of teams, like the Cardinals, Rays, Royals, Pirates, etc. have seen this gap coming and they're building through drafting and developing as opposed to signing up every veteran they can find.
It would be nice to cap the spending to a degree, but in terms of parity, the MLB is up there with other leagues, surprising enough. I say this as a fan of the Cardinals, who are in good financial shape. It's gotta be tough when you are a fan of the Rays and have teams like the Red Sox and Yankees spending 2-3 times as much as your team is and you have to compete with that every year.
I think the Rays are doing quite nicely for themselves. It helps they have the smartest front office in baseball and one helluva manager. Given what he does with what he gets and the payroll they maintain, it's a travesty Joe Maddon doesn't win manager of the year every season. If only they could add a couple of offensive chips, they'd be deadly even with such a low payroll. It's ashame they consistently have amazing pitching but half their lineup can't break the Mendoza line.