The problem is, "We're going back in," doesn't give us any idea just exactly what Buffy's plan for the second assault really was, so it's hard to judge just what she was willing to risk the second time. Certainly, it could have been a full frontal assault, but it could just as well have been a group of Potentials led by Giles or Wood, since Xander probably wouldn't have been up to the task at that time, creating a diversion while she, Spike, and Faith took Caleb on in a coordinated attack, keeping him off balance, never giving him the chance to use his superior strength against any one of them, because whenever he tried, the other two would be attacking from his back and side.
All that we know for sure about Buffy's plan for a second assault is that she believed that it was necessary, and that she was willing to discuss and refine the final strategy. Buffy's chief mistake was that she didn't wait until Spike returned, then taken him, Willow, Giles, and Faith into the kitchen, locked the doors, and worked up a workable plan before springing it on the entire group. Almost as bad was her timing. Xander had just returned from the hospital, probably still groggy from pain medication, and probably not thinking completely straight at the moment (at least his reaction there doesn't seem to support his prior, speech in total support of Buffy and her plans) Poor preparation and bad timing don't necessary indicate that Buffy's ultimate plan was flawed. Te truth is,we will never know just what that plan was, and wihout that knowledge, I find it hard to pass judgement.
I've said this before, and my opinion hasn't changed. What Buffy proposed wasn't a bit different from what she had been doing all season except for one single factor. She had been fighting alone, or with Spike as back up, taking all the risk, suffering all the injuries, while the Potentials sat safely out of harm's way, exercising in the back yard and listening to lectures in the basement. Now, they had had their first taste of combat, of the personal risk involved. of the very real possibility that some of them would die, and they didn't want any more of it. Given their situation, that wasn't really a viable option.Sure, they had encountered Caleb at the vineyard, but that didn't mean that he was for some reason permanently located there. He could just as easily been in that tunnel that Faith led them into, or in that alley where Kennedy was the bait to catch a Bringer. What was different? Pretty much just what I have already said.
The plan to catch a Bringer, and the plan to go into the tunnels, both had two things, and to things only, that Buffy's plan didn't. Before each, the group sat down and discussed strategy, which is exactly what Buffy offered to do before returning to the vineyard a second time, and Faith had the support of Giles and the other experienced people in the group, something that Buffy should have been sure that she had before announcing her intentions in general.
In the end, Buffy's thinking was right. The bad guys were hanging out where the power was. Returning to the vineyard resulted in obtaining the Scythe, which, ultimately, in addition to the amulet that Angel supplied, were instrumental in stopping the First Evil's plans.
I see your points and find it hard to entirely disagree, as this is an area for speculation. However as you state Buffy's 'Poor preparation and bad timing don't necessary indicate that Buffy's ultimate plan was flawed' to me are strong indications that her ultimate plan was likely to be flawed. Poor preparation and bad timing are two of the worst things you can have when constructing a plan, if buffy could not even do these things when announcing that she has a plan, then I have little hope in her implementation and construction of that plan.
Also, yes the scythe did play an instrumental role, but the potentials did not need to die in order to acquire it. How many future slayers could have died in a trip to the vineyard, enough that they would not have been able to hold back the turok han long enough for the amulet to kick, quite possibly, but again this is speculation.
Ethan Reigns
"Prior preparation prevents poor performance" - Maj. Frank Burns of M*A*S*H If that loser can understand it, why can't Buffy?