IMHO, the Winning Alliance Captain should always, always get a guaranteed spot to advance to the next level at every tournament. Otherwise, robot performance is completely irrelevant!
As an aside, I've been pondering this problem with uneven advancement across tournaments for a while. I've recently written an
FTC Qualifier Advancement Proposal for inter-tournament advancement based upon Weighted Ranks. See the proposal for a full explanation of what this is, why it's better, and examples of how advancement would have happened in Virginia had it been used last year compared to how advancement actually happened. I've been asked to generate comparison data for last year and this year so it can be considered for the next season.
I'd appreciate any constructive thoughts on the proposal. I might not-so-humbly suggest that NorCal could adopt this in place of their lottery approach, which would result in the Winning Alliance captains advancing due to their strong Weighted Ranks. MN could replace their ad-hoc system of advancing more teams early and fewer teams late with a system that advanced the top 3 spots (Inspire #1, Winning Captain, Inspire #2) at every tournament and then advancing remaining spots based on the Weighted Rank wildcard system at the end of the tournament season.