Would it be fair to say that the Rangers improved their minor league system at the expense of their major league team, while the Astros did the opposite?
Yes, I'd say that's fair. Although, the gamble seems a little more leveraged in the Astros' situation.
The Rangers dealt MLB veterans for two handfuls of strong prospects, but also dealt one of their own top-notch pitching prospects (Volquez) for an immediately impactful MLB OF (Hamilton). If they don't contend for the '08 AL West title, then they've got a load of kids whom they can either audition in the Show or trade for needs.
The Astros, on the other hand, now have a farm system that resembles the Yankees' barren fields. If they don't win now, then the only hope for the foreseeable future is throwing cash at FAs and waiting for the '08 Draft and beyond to yield MLB dividends (by development or trade). Which is a long wait.
I'm not a Rangers fan, but, living in Dallas, I digest a lot of their organizational information (particularly from Jamey Newberg, whose Newberg Report rivals OWA as a source of quality information). Their MLB and farm situations were absolutely deplorable from about '02-'06. In the Show, they had a lineup full of boppers, a pathetic rotation, and a shaky pen. On the farm, they developed almost
no homegrown pitching. Sound eerily familiar?