I've come up with an idea for an upgraded dowsing rod. Crafting it would require additionally bronze bar (or nugget?) and it would allow detecting quality of water. Detection still capped by survival.
Also I haven't been able to explore underground really that much, so I have no idea about these matters, but shouldn't quality of basic resources, like water or clay, be higher as well? Multiplied by some amount per level of mine? It doesn't have to be much. Patches of sand or dirt could be useful. Making wells underground would be a nice possibility too.
Another nice addition could possibly be another dowsing rod solely for prospecting. As for ingredients it should require something more rare. Perhaps precious metal would be fitting.