Below is a bookmarklet script that allows you to convert Strava.com activity data to a GPX file. Simply drag the button to your bookmark bar.
Then when visiting an activity page on Strava.com simply click the bookmarklet to download that activity data as a GPX file.
This tool is built by a GPS amateur, please treat the output with scrutiny.
There are many incentives to be a paid member at strava.com and if you like the site I urge you to become one to support the company. This GPX export feature is slightly different from the official one and intended to have more customization. Therefore it should be considered as a complement to the official GPX export feature rather than a replacement.