I agree with you, Doug, that the filly races should have some weight toward the Derby since 3-year-olds are so lightly raced nowadays that, as you said, no one knew Dreaming of Julia was that good until her last race, but the list you offer up of the fillies that ran in the Derby doesn't help the argument. Of the list, the only one who hit the board and would have been excluded under the current system is Eight Belles.
2010 Devil May Care- 10th
2008 Eight Belles- 2nd
1999 Excellent Meeting- 5th
1999 Three Ring- 19th
1995 Serena's Song- 16th (won Jim Beam against males)
1988 Winning Colors- 1st (won Santa Anita Derby)
1984 Life's Magic- 8th (ran 5th in Santa Anita Derby)
1984 Althea- 19th (won Arkansas Derby)
1982 Cupecoy's Joy- 10th
1980 Genuine Risk- 1st (third in Wood)
1959 Silver Spoon- 5th (won Santa Anita Derby)
So over half of them raced against the boys prior to the Derby anyway. The Preakness and Belmont aren't relevant as nothing has changed with them.
Again, I agree with you that the Oaks prep races should count, because I agree filly owners don't run fillies unless they feel they have a real chance and it's good for the sport's profile when fillies run in the Derby. I just don't think that the fillies' record in the Derby helps the argument as the two winners would have made it in under the current system anyway, and Eight Belles is perhaps not the ideal poster child for good fillies who would have been excluded(
RIP).