SE has done two things in the past to incentivize levelling roulette.
The Adventurer in Need bonus - but by now, the gil reward is tiny, and the materia7 crystals often aren't even worth converting.
At 80, making poetics and goetia tomestones valuable. But with other methods rewarding more tomestones for less investment - and Eureka removing the relic weapons tomestone from the game - there's little reason to care about these past the 1st or 2nd week of each patch. Their use in crafting doesn't cut it.

Myself, I'd suggest following the tank-mount model, and give out rewards for completing X levelling roulettes while at level 80; or Y levelling roulettes as an adventurer-in-need. Something cosmetic - a mount, glamour, title.