I don't know whether this has already been suggested, but since the (lucky) points awarded for finding artefacts far outweigh points obtainable from other sources (very thematic, of course), why not simply HALVE the VP's awarded for the total value of your artefacts? This then halves the luck swing due to favourable and unfavourable digging. I have no objection to luck in games, except when there are frequently wild swings completely out of your control.
Since I've kept detailed scores of all my games of Thebes, I thought I'd check out how your suggestion affected the scores...
In all but a couple of cases the winner stayed the same, but the scores were perhaps slightly closer together... in the couple of cases where the winner would actually change, it seems to be as a result of congress cards... with players who focused mainly on Congress having a distinct advantage as a result.
Thanks for your valuable analysis of the result of halving artefact VP's in your games. It would seem to confirm my belief that such halving might reduce the sense of outrageous luck - without unbalancing the game. Do you think so also? Or would you for any reason prefer not to do so?
I do think it would reduce the heavy luck factor for artefacts... my only slight concern is that knowledge and congress points might become too valuable... but as long as you go into the game aware of that, then it shouldn't be a problem.