It is possible to extract (unpack) the contents of a WSP package into the file system with use of WSPBuilder. This function currently only supports a full extract of everything, so you have to pick what you need afterwards. The command syntax is:
WSPBuilder.exe -o extractwsp
-Filename : (Optional) Define the WSP file to extract. Default is the last created WSP file from the current directory.
-TargetPath : (Optional) Defines the target path to extract the wsp file in. Default is the current directory.
-Overwrite : (Optional) Overwrite existing files.
WSPBuilder.exe –o extractwsp –filename mypackage.wsp –overwrite true
Warning! I have not fully tested the ExtractWSP functionality in every possible scenario, so please understand.
The function is supported from WSPBuilder version 0.9.9.0728 and forward, including the WSPBuilder 2010 versions.