I recommend you analyze what features you're trying to leverage: camera, GPS, OpenGL ES/Rendering. Also, try and see what code you can reuse to be consistent across both platforms: the AR feature, wi-fi triangulation, and UI (UX will inherently have differences between iOS/Android).
My experiences with the camera include low-level image processing algorithms that 3rd party applications can't really optimize for. This is something from my own codebase that's fairly independent from everything else.
GPS/wi-fi triangulation is tricky because it's more understanding how iOS and Android track your location and maintain state. Whether or not you use a 3rd party application or your own code to parse it is up to you. As with a lot of things, the more you understand, the better decisions you can make ;).
Finally, UI (because I haven't done a lot of Open GL/rendering)... it's a pain to work with across different platforms, so leverage whatever you can to simplify this process. If all you're using 3rd party applications for is to translate iPhone UI to Android UI, go for it.