I'll just add my 2 cents to that as it's the wide consensus on the forum... the digging treasure skill of the pet dragon is pretty much the best skill exactly for the randomness part of the game.
I'm a level 14 Mage (impossible) and that skill is already maxed out (3 treasures for 8 rage).
I'm trying to wipe out Rusty Anchor only with a stack of 2 red dragons (going well so far).
But I still take time (sometimes chances) to dig my 3 chests. I got the great target spell (couldn't find it anywhere in rusty, scarlett, bola, debir and even 3/4 of Verona) and phoenix spell like that. Plus I already got myself 5 runes this way and 3 wanderer scroll... 1 call of colossus, 1 ancient knowledge and 1 depth of tought (which I'm gonna use as soon as I can reach that elenhel guy!)
In my previous game, as a paladin in normal, couldn't find the resurection skill anywhere in debir, scarlett, bola, rusty, verona and Montero. Finally dig it up during a fight against a regular ennemy in Tekron.
So dig up my friend... dig up!