That is a good idea. This is how I manage things:
Every time I release an official update I create a zip of the following in my project folder:
All files in the root folder (includes project files, release note text file, etc)
The Objects folder and all files within
The Files folder and all files within
After creating the zip I rename it to "ProjectName_Official_v2.5.1.zip" (using current version number of course). Then I move it to a "Builds" folder.
The result is that I have intact source code of the exact release as it was published and of course I also have the APK, Java source and the ObfuscatorMap.txt file. If ever I need to look something up from a past version I just look in the zip file. If I want to recompile or examine source code, I just unzip to a new folder and open the project.
I find that this works well for me. Just an idea.