@Dreckitt: That was me, and I just double checked – yes, you end up with a net positive if you spare the nobles.
To be exact, if you kill the nobles mercifully, you get:
-50 to your credibility with aristocrats
-20 to your credibility with merchants
If you kill them as a “terrifying example”, you get:
+4 to anarchy
-100 to your credibility with aristocrats
+30 to your credibility with helots, but only if you have the aristocrat background
-20 to your credibility with merchants
If you show them mercy (either path), you get:
+10 to your credibility with aristocrats
-10 to your credibility with helots
-4 to anarchy
-5 to morale, if your Charisma isn’t 3
In all cases, assuming you are successful, you get:
+6 to anarchy
+15 to morale
+120 to income
For scaling purposes, the range for credibility in the portion of the game that currently exists is 0-200. For all factions other than Helots, a score greater than 200 represents “Might not be /all/ bad” and 0 representing “My worse enemy”. Helots, on the other hand, consider scores greater than 200 to be “A hero in waiting” – in short, it is much easier to get the Helots on your side.
Note that given the way the scale works, the +10 makes sense, in my opinion. First, +10 isn’t all that much. Secondly, the best you can hope for in Chapter 1 is to make the nobles think that you are someone who they /might/ be willing to deal with – that is, yes, you’ll take what you need and you have a definite agenda, but… You aren’t /necessarily/ hostile to nobles, at least to the degree that you’ll kill them on sight.
In that context, then, I feel that the adjustment makes sense. The only caveat I have is, like I said, earlier, the game should point out the possibility of showing mercy during the “Are you sure you want to do this” message block.