Any question answered...

Is there any free software/sites/apps that can do this:

-show up to 15 rides gpx routes together onto a single google map type background with full zoom in and out ability
-show the routes in different colours so I can tell each ride apart. I know veloviewer lets you group multiple rides on a page but they are all one colour so its hard to distinguish one ride from another?
-be able to add in multiple points/labels along the gpx route so they show on the map, like points of interest/pubs/cafes etc

Does such a thing exist? It all sounds perfectly feasible in my mind, but there's often a disconnect between that and the real world.

Garmins very own basecamp can do all you require.
http://www.garmin.com/en-GB/shop/downloads/basecamp