Tuning the "Go Back" was hard. Originally I had it tick over a square 10 times per second, but that seemed too fast for the first few zones. I think a good mechanism, in hindsight after resting after the jam, would probably be to make it faster as you go further through the board. I.e. first 1-5 you go back per tile 2 times per second, but once you reach the boss room it goes at 15 times per second? Worth exploring.
You also nailed one of the optimal builds. Another tweak that should be made is raising the "Min" cost of the dice and also raise the price of a crit. Probably 30G for min raising and then 70G for crit raising? A minor nerf would go a long way to encouraging dice variability.
But I think ultimately I'd want there to be more variety so there isn't just *one* optimal build. I like games that the player can "break", so introducing more build ideas would be my preference :)
Thank you for the kind words!