I haven't decided if I'll just send them an email or snail mail (w/ a small Dunkin Donuts giftcard), but I plan on thanking them again and telling them about my accepts/rejects etc. when this is all over.
As an applicant to both programs, my impression is that both programs (in terms of Social Psych) are fairly eclectic. It does seem to me that Princeton does have a disproportionate number of people working in prejudice, intergroup relations, stereotypes, etc. Regardless, you should read the faculty bios of both institutions and decide which would be more in sync with what you're looking to investigate.
That sounds exactly the kind of work that two grad students (and I think a honors thesis student?) I know at Rutgers University have done. They both have worked under Lee Jussim and (I think) one also worked for David Wilder. You might want to look for them.