OP-- I am also an IPE person with similar interests to you, and I agree with the post above. It's definitely worth it to apply to Harvard/Princeton/Stanford; even if the odds of success are low, the payouts are high. I thought like you did, and now I regret not applying to more top schools.
I applied to some of the same schools as you, and decided to go to UCSD. UCSD has a really solid IPE group and they work together really well. If you're familiar with Frieden, Lake, and Broz' IPE textbook, well, you've got 2/3 of the authors right there. There's also not as strong of an "IPE/Security" divide as at some schools; people like Lake, Gartzke, etc. work in both fields. And the comparative and IR faculty work together too if that's something you're looking for. Plus faculty in the policy school (GPS) are almost all traditional academics and open to advising and working with Poli Sci students, which expands your possible faculty mentors significantly (this is a big difference from schools like Harvard, Georgetown etc. where poli sci and policy school are separate, or policy school faculty are former diplomats and such)
I also visited USC and I actually think the program is far better than its ranking would suggest, and they are well funded and expanding with lots of new hires. It may take them some time before the rest of the discipline realizes this and adjusts their perception of USC accordingly though.