Indeed. I'm creating GPX routes for Audax Organisers that aren't GPS savvy (reminds me, need to finish off a couple based on final tweaks). When looking at what people use I found:-
Audaxers use GPS routes in various ways:-
1) Minimalist route (one route point at each junction)
2) Minimalist route (one route point just before each junction)
3) Minimalist route (one route point just after each junction)
Then there are those that use tracks:-
a) GPX tracklog for the entire ride (out and back or including loops)
b) GPX tracklog for each section between controls
c) GPX tracklog split into logical segments (one for out, another for back, or done per day, etc)
each of which may or may not be required to be reduced to 500 points.
Users of GPSes that take non-standard stuff:-
i) Extended GPX route containing thousands of points (using GPXX extensions) for the Garmin Edge 705
...etc...
So the simplest answer, when having to provide just one thing, is a single GPX file that contains one or more tracklogs each reduced to 500 points and split at a logical point (half way usually).
GPS savvy people will then be able to munge it into whatever they want, but the average person just wants something to upload to their GPS and go.