I think Texas has a very good test case for the academic benefits, or lack thereof, of being in a P5 conference, and that's a comparison of SMU and TCU. Those are very similar schools with good reputations but not elite, somewhat selective admissions and equal fundraising. Both are roughly private versions of Miami of Ohio: safety schools for rich preppy kids. Has TCU separated itself from SMU by any significant such as student selectivity, rankings, fundraising?
WIKI doesn't data for Houston, Texas St, or UTSA, but I do have data for Texas, Texas A&M, Trinity, Rice, SMU, Baylor, and Texas Tech. The following is the average percentage growth rate of their endowments:
For the 5 years from 2007-2012 (which includes some bad market years)
P5 Schools +2.8% (Baylor, UT, Texas A&M, Texas Tech)
Non P5 Schools -1.3%
For the 5 years from 2012-2013
P5 Schools +6.9% (same as above, plus TCU)
Non P5 Schools +5.5%
There isn't much difference between the three teams that originally were excluded from P5. Here are the first five and second five year numbers for them:
Rice -1.1% +5.6% (stayed in CUSA)
TCU -0.1% +5.2% (Jumped from WAC to Big Twelve)
SMU -2.4% +5.2% (Jumped from CUSA to AAC)
Trinity -1.7% +5.6% (Not Division I football)
The ones that were clearly higher than the rest were the UT, Texas Tech, and Texas A&M.