Using a binary library is always a nightmare. That aspect in Cocoa is terrifying after Java. With all that openness I really don't understand why Cocoa is closed-source. They could open it with "read only" license, it's not like someone could get any benefit from it.
To make working with the assembly code easier, I've found Facebook's Chisel (specifically the "pinvocation" command) to be really useful: https://github.com/facebook/chisel
Chisel is awesome. pviews is another great command, it prints the view hierarchy along with the object addresses so you can easily send messages to a specific view. This is handy for changing properties during runtime, for example.
I don't see why the debugging had to take place on 32bit binary. From experience, the debugger disassembly for 64bit is much more "readable" - as in much of the symbols called are spelled out a lot more, and accessing function arguments are much much more friendly - "po $arg1" instead of register math.
Hopper is capable of parsing 64bit disassembly and create pseudo code from that as well, if you need it.
Author of the post here: this was my first serious foray into disassembly land and I remember one post pointing out that Hopper had a harder time with disassembling 64-bit slices. However, it appears that was wrong! About to add an update to the post.
[1] http://accidentallyquadratic.tumblr.com