You should be able to use something like this to load, save and access your settings:
history_filename = 'YourPluginName.sublime-settings'
history = sublime.load_settings(history_filename)
value = history.get("some_key")
The file will be saved in Packages/User/YourPluginName.sublime-settings
EDIT: Using this method takes advantage of the code built into SublimeText to handle reading, writing and caching of the settings files. The settings are stored in a JSON formatted file.