ModRana is using the upoints module for inmport and export of GPX. Upoints uses the standard Python ElementTree module for, which is what adds all the 'ns0', which should be harmless but looks ugly. I haven't yet got to testing the files created by modRana in other programs, so I'll look into it now. Considering timestamps, that is planed together with elevation, point name and description.
OK, ticket added.
Yep, its like this to simplify the drawing algorithm. I think it could be extended, but IMO viewing the whole world on the screen is not a very often used feature. I added a lower priority ticket for this.