by Ranior
Very interesting numbers all around.I too would guess most of the Swarmlings games are just for VP's. With high priest production and generally good coin production throughout the game, I can see how advancing digging earns more points than building your comparatively "expensive" buildings. Be curious how many of them are before R6.
Largely same thing with Chaos Magicians as DocCool already covered.
I'm kind of guessing many of those Witches games though are actually using their upgraded digging. In certain match ups I find I get plenty of green hexes early due to so many being available with 1 shipping, but from there it can hard to secure all the needed hexes to make three towns if you're not lucky enough to get the perfect set up for the easy town locations. If you're in that situation you also need to be using some power for bridges, leaving even less for spades. And you need those towns to do well in general. I know I've upgraded digging sometimes in the mid game with Witches to some success.
Which I guess goes back to the OP's original question which Steve covered so well--but basically most factions shouldn't bother. There are a few factions which almost always should, but outside of them it's pretty rare that I think advancing digging is ever the right move outside of late game VP's. (And even then I think in general it represents you've played a bit poorly if the best you can do is convert all those resources to 6 points given they are practically worth 3 points in just direct coin conversions).