This is exactly right. There have been various interviews with college admissions directors over the past year, and they pretty much all said the same thing. To paraphrase, "We expect that AA will be struck down. If we can't directly ask about race on the application, then we will achieve the same result by indirect means".
AA opponents mistakenly believe that colleges will now be forced to consider only grades and test scores. Nothing could be further from the truth.
Colleges give preference to legacies because the admissions department is judged by its yield (the percentage of accepted applicants who actually enroll), and legacy applicants are more likely to enroll if accepted.
It's not necessarily related to being rich. A legacy is about as likely to be wealthy as other students at the school, because after all their parents were also students at that school.
Another important reason is that colleges rely on alumni donors, and alumni are less likely to donate if their children are not accepted.