Sorry PG, I have to really question you on this.
Education, mentoring, and team building all happen better in smaller environments. Things like class size, team size, and time spent matter. Maybe what you mean is the actual time spent with each participant is still the same per investment as it was with smaller classes (i.e. you're all putting in more time than you used to) but somehow I really doubt this. I'm also sure that certain partners have certain strengths weaknesses that benefit in different areas and not having as many partners advising different startups would be less value.
That said, I'm sure Ycombinator's value is still great compared to other incubators, I just don't really feel like the statement "we're scaling just fine" on a squishy, hard to scale item like "advising" to pass the sniff test.