"Ticket to Ride: Europe": how to accommodate differences in players' strength?
Increasing the number of cards flipped on tunnel routes should be considered.

Likewise, one can readily balance things with a requirement for more cards per track segment. For the most experienced, increase the card requirement by 2 per chunk, but do not increase the score. 1 additional for the more experienced. It's brutal, but changes play very little, just the length of time it takes to be able to claim a route.