As far as I know there are no tools for exploring and interacting with .IPA files like Androguard for.APK files, but since the .IPA is essentially a zip, you can unzip and analyze the key components individually.
Key components of the file and associated tools include:
The Mach-O file contains the executable code. This executable is encrypted inside the .ipa file unless it has been dumped and rebuilt from a rooted device. Once dumped and rebuilt the functions, strings, etc. can be viewed with IDA Pro. Objective C can be hard to follow so plug-ins like https://github.com/zynamics/objc-helper-plugin-ida can be helpful. Also, check out otool and class-dump http://www.codethecode.com/projects/class-dump/ .
For gathering interesting information I have found the plists (especially iTunesMetadata.plist and the Info.plist). Plists found in the .ipa will either be in a readable XML format or a binary format. To convert binary to readable XML use Apple's plutil(1) or plutil.pl.