Cleaning/editing GPX (tracks) files recorded from GPS device in QGIS?

I'm also searching for a really good way to do this... but in the meantime I do have a system which works OK. Slow but effective:

Use the Openstreetmap editor JOSM. This is good at displaying GPX info. Use the plugin 'InfoMode'. This makes it easy to see the time data on the GPX track. Note exact times for the nodes which you want to edit/delete etc. Edit the GPX file by hand in a text editor which is good at displaying XML files (or a specific XML editor of course).

Note that JOSM seems to take account of local time - so for me it shows times in UK summer time - whereas the GPX file has times in GMT/UTC.

Being able to use 'regular expressions' with the text editor helps if it turns out that your GPS has inserted additional useless information into the GPX (which you want to delete).

I upvoted @user27285's answer. I don't know any better. I use the Josm editor with the EditGPx Plugin and other JOSM features to edit my gpx traces all the time. You can configure Josm to show when your track changed directions by color styles. On top of all those features you also have reference Imagery layers to pick from to help see where your data is located.