In my post about XP for HD last night, my buddy Josh makes a good point in the comments.
My goal of increasing XP per HD at the low end of the scale was not to increase the value of fighting (so you only need to kill 20 orcs to level up instead of 400), but to increase the speed of leveling.
My preferred style of play is to encourage creative ways to get the treasure without resorting to combat more than it's necessary. So why not stick to the original XP values for combat, but institute XP awards for outwitting/outmaneuvering/trapping monsters than killing them?
Of course, in this case, I'd not want to give XP for the combat prowess of the monster, which is what XP per HD (bonuses for special abilities) does.
Taking a look at AD&D's descriptive levels of monster intelligence, it wouldn't be hard to institute something like this:
Animal Intelligence--25 xp
Low Intelligence--100 xp
Average Intelligence--200 xp
Very Intelligent--500 xp
Highly Intelligent--1000 xp
Exceptionally Intelligent--2000 xp
Godlike Intelligence--5000 xp
Of course, these would be awarded per group, not per individual outwitted.
Other useful side effects would include more XP for using a Sleep spell but not slitting throats immediately after, making me as a DM pay much more attention to the Int. level of all monsters when I roleplay them, allowing more ways for the Thief to shine, and giving more reasons for M-Us to memorize non-combat spells.
The downside? Big HD but low intelligence creatures. If you're out for XP, why try to outwit the 20HD T-Rex (other than to avoid its terrible bite and almost guaranteed chance to hit each round) if outsmarting it is only worth 25 xp?
I'll need to think about this a bit more before implementing it, obviously, but it may be a step in the right direction.