I've been looking over the death spells, seeing how I can change them to not be so "save or suck".
Now, one thing I've done is to change the death/dying rules so that a) you die when you hit negative Con score, not -10; and b) each round, you make a Con check to stabilize; if the check succeeds by 0-5, there's no change; if it's 6+, you go to 0 hp, and if it fails, you lose 1 hp. 3 failures and you die.
So, with death spells, what I did is instead of "save or die", it's "save or be reduced to dying, but you automatically fail the stabilize rolls". Which means there's still a good chance of dying if your friends don't get to you in time.
One other idea I'm toying with (and the reason I'm posting this) is putting a HD cap on what can be affected by a given spell level (like the damage caps). For instance, circle of death is L6; it affects 1d4 HD/level (20d4 max), with a 9 HD cap. So what I suggest is:
L6 single-target: 12 HD; multi-target: 9 HD
L7 single-target: 15 HD; multi-target: 12 HD
L8 single target: 18 HD; multi-target: 15 HD
L9 single target: 21 HD; multi-target: 18 HD.
These caps are for arcane and divine - there's no difference.
Thus, a spell like wail of the banshee could kill up to 1 creature/level that has no more than 18 HD.