I'll be starting CIPA in the fall for the following reasons:
1) Flexible curriculum. I know exactly what I want to study and have access to every graduate department at Cornell. I'm interested in environmental finance and market-based environmental policies, so having access to Johnson finance classes in addition to atmospheric science and ecology classes is fantastic. If you can argue that a class aligns with your interests the administration is willing to listen.
2) Very generous funding. You won't find funding this good at other programs. Instead of facing debt and penny counting in grad school, I'll be able to relax a bit.
3) Strong faculty/alumni support. There are some unique perks to CIPA being newer; CIPA has every reason to make sure you're successful because they want to grow the program. After speaking with CIPA folks I was impressed by their level of personal involvement and interest in my career.
4) Close program internally. Ithaca's isolated, but this also forces you to become very close with your fellow CIPA's. The fellows I spoke with were very friendly, welcoming, and mentioned how strong their internal network was.
5) Cornell's network/brand. It's not just restricted to CIPA---Cornell's alumni are very supportive and the network is huge (I was an undergraduate there). I wouldn't worry too much about the ranking; it's a top university with stellar professors and alumni and you will work your butt off. Furthermore, Cornell's future direction will be more internationally focused ($2 billion international NYC tech campus is evidence of this) and Cornell already has strong presence abroad (Ithaca also has some pretty good Asian food because the campus is so diverse--it's like a little multicultural microcosm).
How to think about rankings:
MPA rankings by US News are a function of peer assessments of other MPA educators (deans, facutly etc). The quality of peer assessment is usually the result of academic visibility in public affairs publications. And here is where CIPA is unique among MPA programs; it's an institute rather than a school. The strength of this is that CIPA is interdisciplinary, flexible, and you have access to every graduate class at Cornell. The weakness of this is that CIPA faculty are usually published under different departments of Cornell! Thus, although the work that CIPA folk do are the same, visibility of CIPA is lower because this work is published under different titles. That's not to say MPA rankings are entirely worthless--peer review is very important. HKS and WWS are ranked high because they are, indeed, amazing programs. However, when considering CIPA, the nature of the program is likely a barrier to higher rankings, when in reality, in terms of quality, CIPA is likely much higher than what the rankings show. Also, after attending open house, about 25% of this year (so 2014?) applicant pool was accepted. That's pretty solid.
Consider this fact; Cornell's grad programs consistently rank in the top 10. CIPA is in many ways a focused slice of the "Grad program" pie at Cornell. Just a simply heuristic like this makes me think that MPA rankings, in general, are far less accurate than MBA or Law school rankings (but once again, the top of the top MPA programs are up there for good reason even if ranking methodology is imperfect--think of peer review as a endogenous variable; if there is an overwhelmingly strong correlation of other "hidden" variables like in HKS and WWS, the effect of these variables will eventually be strong enough to influence "peer review" in that direction).
In terms of quality and opportunity, I wouldn't worry about CIPA's rankings if you think about it. But regardless of your decision, I firmly believe your success is ultimately up to you. "Ivy league" universities can only put a few more opportunities in front of you; ambition, hard work, and tenacity are the values that really matter.
PS; With CIPA, you can spend a semester in Nepal, DC, Rome, and I think somewhere else...