Yeah, it should be fine. At low levels (where the boost will be most noticeable) It would be about comparable to what you could do with a basic greatsword hit- admittedly on a ranged touch attack, but then, you'd have sacrificed pretty much every other capability to accomplish that.
You can boost your charisma later on to get more out of it, of course- but by then, you'll have even better options for damage than one of my essences. The favored Vitriolic Blast, for example, is going to outpace all but the highest charisma modifiers.
Thanks! I felt just a flat bonus would be a bit boring and might be a little low, but didn't want to increase it too much.And as usual, nice touch adding the "two hand" option, it works perfectly.
Incidentally, I've been thinking about a non-eldritch blast warlock. I'm not sure this will be quite what you were looking for, and I'm still a little unsure about balance, but I just wanted to get it out here:
EDIT FROM THE FAR, FAR FUTURE OF ONE YEAR LATER:
I'm going to leave this intact just for the record, but note that the following ACF is not something I consider complete or balanced (which is why it has not been moved to the first post).
Mystic Curse
Class: Warlock.
Level: 1st.
Replaces: You do not gain Eldritch Blast.
Benefit: You gain the ability to curse and debilitate your enemies. As a standard action you can make a ranged touch attack against one target within 60ft. On a successful hit, you deal 1 subdual damage to the target. This is a first level spell-like ability that allows no saving throw.
You may apply eldritch essences and blast shapes to your mystic curse as if it were an eldritch blast. However, you may apply a least eldritch essence to your mystic curse in addition to any other essences and blast shapes you apply. This also allows you to apply the same effect twice, though this is not beneficial in the case of all eldritch essences. The effects of each essence are resolved separately. If you imbue your mystic curse with two different types of damage, half of the damage (rounded down) is dealt by each source. You must choose which essences you will use in conjunction with your mystic curse before you start your action.
At 9th level, your additional essence may be either a least essence or a lesser essence. At 17th level, it may be a least, lesser, or greater essence.
At levels 1, 3, 5, 7, 9, 11, 14, 17, and 20, you learn a bonus eldritch essence or blast shape invocation of any grade available to you. If you choose to replace these invocations when you level up, you may only replace them with essences and blast shapes, not other invocations.
A few thoughts on its balance: It grants a ton of bonus invocations, but essences and blast shapes do tend to be a lot weaker. The ability also needs extra essences in order to equal eldritch blast in power, since it doesn't actually have any ability of its own. That said, it may still be a little much. I might lower the number of extra invocations it gets.