If there was any skill involved or anything else than just pure luck involved in finding artifacts I think it'd be ok to give a bonus for it, however finding an artifact will usually be pure luck or linked up to some situation in the dungeon (vault or unique) that already gave you more experience. Also, since most artifacts will help your character survive longer I don't think you should get bonus points for finding artifacts.
If anything you should get a score penalty, since you've had an easier route than some poor guy with a broken sword and a ring of aggravate monster. ;D
As for unique kills, they already give good exp and some of them have great drops, but... I don't think we should increase the experience they give, that'd just make the game easier, but maybe there should be given bonus points for killing a unique thats much stronger than you, say - a lvl 9 paladin spending 90 minutes trying to kill Wormtongue and finally, YEAH!
This could be based on the monster/player level thing, the same way protection from evil does it, resulting in a number that again could be multiplied to the Ironman score. I don't have access to the protection from evil calculations here or the monster levels so I'm not sure if the result of monster/player would be a figure that's comparable to the Ironman Factor. However I suspect this is would be harder to balance than the IF in my post above.
Two examples, with random incorrect values.
Player 12 character kills Brodda.
Say Brodda's level is 15, so 15/12= 1,25.
This would give a number that could be used, I guess.
However if a lvl 15 character kills Uldor, a rather deep but not very hard unique he could end up with 35/15 = 2,33 which would seem too high.
Maybe if the game kept track of all unique kills for each player and their monster/player score and combined the results into a value that would make sense to multiply to the total score or ironman factor.
I don't know how others feel but to me it seems wrong to reward a player twice for killing something once.
Maybe there should just be a "Uniques killed" highscore instead, possibly connected to the character dumps.
Or maybe the "~" (unique monster page) should display not only who has currently killed each unique but also the top 3 killers of each. I don't really like that idea though. It'd just tell everyone who's been playing the most and you can see that already by hitting "@" or "#" or checking out the Ironman Ladder.
It's still early here and I haven't slept much tonight, so, forgive me if nothing of this makes sense.
-- Mangband Project Team Member