You could free-ride onto Spa or KartSpace when it came out (including joining a room and making someone elses lounge when they weren't in it), but the next update killed the freerides for those tracks.
You can currently get on Route X without purchase (I have multiple times), I suspect they'll de-allow that with next update.
Seems to me they do this deliberately to have a try-b4-u-buy ... temporarily.