Jim -- I think this is at least as much a symptom as it is a disease. If after eight years of watching Astros minor leaguers, the average Express fan has not been co-opted as an Astros fan, then management (both Astros and Express) has really screwed the pooch.
They should make a bigger deal about Astros players and scores at Express games and in Express radio broadcasts (and for Hooks as well).
They should figure out how to get Astros radio broadcast locally ... if all it takes is money, then sponsor the broadcasts!
They should also bring back the exhibition appearances both between Express & Hooks and between the Astros and their affiliates.
I'll go watch the Express (at least some of the time) regardless of affiliation, because I just like to watch minor league baseball. But I will go a lot more often if they stay with the Astros, and it would be a lot easier in general to keep attendance up if they actually tried to emphasize the tie-in.
Most of what you're saying is because of an odd convergence of multiple situations:
1. Odd radio and television rights here in Austin (and I'm not sure about Corpus Christi) that doesn't favor the Houston Astros entirely. There is more media presence for the San Antonio Spurs basketball than there is for the Astros baseball. While the Spurs do not come close the University of Texas in terms of media exposure, they certainly are not a woeful second place media driven presence. I think more could be done to bump Houston Astros baseball to the very least the Spurs level of exposure (IMHO of course).
2. The Express (don't know about the Hooks) are in this as a business first, minor league affliate second and they do a damn good job of the former and latter. But they focus on the entertainment value for the general fanbase here in Austin. That means while I and many others are interested in the development of Houston Astros prospects, many of the fanbase here in Austin are interested in the entertainment ROI for the family. It is a wonderful experience for the family to attend an Express game, that is the way Reid Ryan works well.
3. The Houston Astros baseball ops may be running their minor league system with just a tad too much business acumen and not enough relationship fostering in mind.
All three lead to a less than growing presence here in the Austin area for the parent organization but certainly the Express won't lose much because they've managed to focus on growing an entertainment outlet here first, a minor league affliation with a beloved team second. See, the Houston Astros are no the Boston Red Sox or St. Louis Cardinals in terms of a following (yet), so the Ryan/Sanders group knows they won't get much bang for their buck by giving too much up on their end to the parent organization today. In the next ten years? Perhaps, if this organization (Houston Astros) finds itself doing consistently what they've managed to do in the last 10-15 years. The following will be strong and play very much into the negotiation process for anyone wanting to be associated with them, from radio to minor league ownership groups.
Today, the Houston Astros can't afford to act as if they're already there.