I really love the concept of sidequests at max level giving something extra. WoW made a change years ago to give extra gold for doing any quest at max level; FF XIV could give tomestones and/or Bicolor Gemstones (as gil practically falls from the sky doing various content).

As for roulettes, I tend to only do Expert, Alliance, and Normal Raids (being max level on all jobs). They seem to be the best bang for your time in terms of tomestone -> time ratio. Sometimes MSQ roulette (big win at max level drawing Castrum as all the cutscenes but one have been removed and the trial is a slow). Rarely the "Level cap" roulette. Trials, unless you get an older older one (aka Stormblood or older) just take so much time for a puny amount of tomestones. Levelling be a real drag if you draw an ARR one where your job kit is sliced down to bare bones.

I never done a hunt train but yeah, seems like the vast majority of forumers say that's the way to go. Just a matter of a train being available at your playtime. Cross DC'ing making it worse as trains can just hop worlds over and deplete every server in a region.

Challenge logs would be good too. Something similar to what Cosmic Exploration does, where doing certain things gives points and finishing enough of the log would give Tomestones/Bicolor gems.