Thanks for the ideas!
Wood and Coal exchange will be coming in the next update, and I'm also planning to add a Titanium exchange later on.
For the slot machine, I agree that some kind of pseudo-random system could be a great addition. For example, if the average jackpot hit rate is around 1 in 593 spins, the system could start slightly boosting the odds after your 500th spin to help out us unlucky folks. I've personally burned through thousands of quartz without landing a Reeler, so I definitely feel your pain :")
Instead of upping gem spawn chances across the board, I'm thinking of other ways to help, like adding quartz to a zone that currently doesn't have any, or introducing other gems into the Magma zone, which do feel a bit empty right now. And you're not alone, getting to water with Nix is definitely tough. Even Lynn Xternal, our top Serenitrove player, mentioned how challenging it was.