I don't think Paul's point is that YC is incredibly valuable because of the support network, although that is definitely a factor. Its that you won't get screwed around by investors as much and simply in terms of seed/Series A valuation differentials between YC and non-YC companies (all other things being equal) you'd probably be getting a better deal (in terms of equity ownership) even if YC's average valuation was 50% what it is.