I'd strongly recommend taking a look at
Portals of Phereon in terms of proc-gen driven replayability.
That game is far from finished, but even now if you do a single short 30-day playthrough you won't touch a fraction of all the possibilities the game offers. Meaning you're not playing for grind, but actually constantly finding new elements to experience.
To me, that's a core feature in terms of maintaining players' long-term interest, but I can appreciate that not everyone likes games that demand more than one session to get everything out of it.
Sure, it has a rather different focus than your game, but maybe it'll provide some food for thought.
Niiice. That unique art style certainly sets TT aside from the pack