There are some reasons to like SDSU - chief among them being the continued presence in SoCal. Some of the other G5 options mentioned before (UNLV, Nevada, SMU, Fresno) have various things going for them. But, in the area that really matters ($$$) none of them are even close. Even the ones that are in big TV markets don't draw viewers. None of them even reliably sell tickets. The Pac-12 already has a pretty low revenue distribution, and none of those alternatives even come close to bringing what they'd take.
It's been suggested that some of them - SDSU & UNLV in particular - would draw better if they were P5 teams. That may be true....but they'd have to draw a lot better to financially pull their weight. And...when the other conference schools are already in a position where they're falling behind, why would we bring in anyone who's going to water down the distribution further?
I'm not even sure that any of the remaining Big 12 teams would be very certain to bring enough value to prevent reducing everyone else's share.
The Pac 12 needs to at minimum expand to 14 teams.
The Pac 12's failure to expand to 14 teams is why they are now the Pac 10 in this mess.
The Pac 12, has to be doing action, expansion, because it will stabilize the Pac 12 because:
1. Even if it's smoke and mirrors illusion, it at least gives the appearance that the Pac 12 is stabilizing, growing,etc.
2. Point 1 above, can lead to bigger, better media deals, with more money to be split between Pac 12 colleges.
3. Because of points 1 and 2, it can make the Pac 12 more Palatable to a Pac 12/ACC Alliance, joint media deal, merger, etc.
4. The Pac 10 is more VULNERABLE to be cherry picked by the other conferences then a Pac 14.
5. If the Pac 10 does get cherry picked, going from 10 down to 8 or down to 6, is WORSE then going from Pac 14 down to PAC 12 or down to PAC 10.
6. The Pac 12 can survive Cherry Picking better.
7. It can make it easier to Cherry Pick the Big 12, instead of the Big 12 cherry picking, killing the Pac 12.
8. As already been said, SDSU, etc, CAN GROW IN VALUE to the Pac 12
9. It's not any one of the points all by itself. It's ALL of these points COMBINED TOGETHER.
10. Expansion can lead to interesting match ups, and can make the conference tougher, which can lead to play off appearances, better bowl games, better media deals, more prestige, more popularity, more research grants, more student enrollment, etc, which CAN LEAD TO MORE MONEY.