*Sigh* Ok. I guess I haven't said everything as clearly as I might have, so I'm going to try to go through it all point by point. I'm also going to try to be diplomatic about this, but if I seem irritable, it's because I am.
1. Regarding separation/extraction of specific elements: yes, some things will have to be developed to fit both settings - but only those elements that fit in both settings. Magic is a part of both settings, and works similarly; virtually anyone can find and cast a spell, but it takes skill, will and power to cast it successfully. Combat is a part of both settings. Cutting-edge technology is a part of both settings and villains of low to nigh-omnipotent power levels are a part of both settings. Gargoyles are a part of one setting. The Slayer is a part of one setting. Details such as these will remain constant, will not be developed with the other in mind, and may be removed and separated with relative ease.
2. Regarding balance: both shows are, in my opinion, similar in terms of power levels. You have relatively normal humans, supernormal humans, and nonhumans of moderate to great power. All the characters improve over time: look at Buffy, Willow and Xander in Season 1 and look at them again in Season 5. (Actually, look at Willow in the S6 premiere, which I consider to be about the height of her power - before she succumbed to her addiction.) Likewise, look at Lexington, obsessed with technology, in Season 1 and Lexington the technology expert at around the end of Season 2. As for the gargs themselves - they would have to have a level adjustment trait no matter what, and I think the exact adjustment would be about the same.
3. A side note: elements from both settings will likely be altered or ignored. I think that will happen more with the Buffy part than the Gargoyles part. I've said it before and I'll say it again - I do not see magic as inherently addictive, so assuming the majority of the developers agree with me, the whole "magic is a drug" bit will be discarded. (And it seems clear to me that it was magic, not power, that was the problem for Willow; certainly that was made clear towards the end of S6.) In fact, I'm prepared to ignore the bulk of Season 6 for the purposes of this setting, if the others agree. (On the Gargoyles end, I think the part that's most likely to be ignored is The Goliath Chronicles - for the most part. I'll get back to that. I'd also like to bring in some clans that might not exist in the present day of official universe - Irish gargs, for example - but that's a personal whim and may not come to pass.)
4. Regarding your final comment, Umbran: I am trying to consider that in my work. Perhaps I haven't made that clear. Perhaps you'd like to tell me what I could do to satisfy you in this regard, because at this point, I don't know. I have invited you to come on board and work not only on whichever parts of the main project you're comfortable with but also on a section discussing which elements belong, properly, in the Gargoyles universe and how to run a campaign set solely in that setting. I will extend that offer again; heck, I will up the ante. If we're going to have people doing all this work on Gargoyles-related material anyway, why not spin it out at the same time into a separate Gargoyles d20 document? I see Claw & Stake as the main thrust of this project because that's the campaign I plan to run, but I see no reason why the bulk of our work can't be applied in favor of those fans who want Gargoyles on rye, hold the Buffy, as well.
And, once again, I see even Claw & Stake as Gargoyles with Buffy frosting. The tone will be closer to Gargoyles. The main setting focus as I see it will be the East Coast (specifically New England and, to a lesser extent, New York), and I see that as a more Gargoylesque region, all in all. There are only two Slayers, and both are in southern California. There are - let's say a few hundred Gargoyles worldwide; based on comments made by producer Greg Weisman (who's currently answering questions about the Gargverse through the medium of Ask Greg - I'll post the link if you don't have it), I'd say there are more clans out there than we've yet seen. In both settings there are humans who fight the good fight - or the evil fight, in some cases. Will there be demons and vampires? Yes, but why can't such beings fit into a Gargoyles framework? Will there be an Initiative? Yes, but clandestine organizations have been a part of Gargoyles for some time - just look at the Illuminati, and to a lesser extent, the Quarrymen. (Like many fans, I consider the first episode of The Goliath Chronicles - the only one written by Greg - to be canon, so the Quarrymen exist, to my mind; but the episodes that follow are...questionable at best. Still, I think the implication that the Quarrymen aren't exactly in full view of the public was there from the beginning.) Look at the secret parts of Nightstone Unlimited. My point is: as I see it, Gargoyles will truly be the dominant element. I just think that certain elements of Buffy would work well with it, even though they aren't absolutely necessary; it gives me and the others a chance to exercise a little more creativity than we'd be able to if I tried to remain true to either universe; and it's something that would be fun to try.
But as I said, I would love to work on a separate Gargoyles d20 manuscript, using the Gargoyles-appropriate material from Claw & Stake. I would love to have your help with that. Given that all this work will be done anyway; given that there's plenty of material on both universes out there; there's no reason why we can't try to satisfy more people. And if this doesn't satisfy you, perhaps you could try to tell me what, exactly, would?