The question of the "correct" date on which to hold winter solstice events has the character of a hyperstition, i.e. it's not really important right now, but if we argue about it enough we can make it important, if that's what we want.
You might say:
To these we can also add a fourth ("Mu") option, to wit: "The date of the solstice event is unimportant and we shouldn't try to make it important."
(To be honest, I put a fair amount of weight on this last option myself; the rest of this post is somewhat speculative. Also, in general, you should be on the lookout for sneaky attempts to polarize an issue by setting up an n-chotomy and then hyperstitiously asserting that your choice there correlates with a larger cluster of beliefs/values. This is essentially what I'm doing here, but at least not sneakily.)
When choosing a date, it mostly comes down to who your target audience is. The Earlybird position makes sense if you're planning a "destination solstice" like the SF Bay or NYC, where you're looking to get visitors from out-of-town. If you're aiming it at people who live in the area but leave to spend the holidays with their families, then you'll lean towards the Last-Weekender position. But by contrast, the Astronomical position conveys the message "We are your family; this is your home."
This last one might seem a bit scary and culty. I want to at least put it forward as a plausible option (since Austin has been doing this the last few years, while as far as I can tell no other communities have held solstice events on weeknights), but also open up the debate about whether it's a good idea.
Halloween is invariably celebrated on October 31 and has stubbornly resisted attempts to move it to a more "convenient" weekend-night. Practically speaking this is due to the coordination problem - if you unilaterally go trick-or-treating on any other night, you'll come home empty-handed; and if you try to give out candy on a different date, you'll get egged on the 31st.
But I don't think that's all of it, at least for me. If I imagine a world where this coordination barrier is somehow overcome, my emotional reaction is not "Well that's a relief" but rather "This is sad - have we forgotten the True Meaning of Halloween™?"
(Do you have a similar reaction?)
It's not because of religion - I'm not a Samhain-observant Celtic pagan and I've never known any such. And it's not nostalgia either - while I have fond memories of Halloween as a child, having to wake up early for school the next day isn't one of them. "Tradition" is getting warmer, but that's still a bit vague. More specifically, it's something like this:
(Incidentally, some time after I aged out of trick-or-treating, my town instituted November 1 as a school holiday because they knew all the kids would be half-asleep anyway. This would never have happened if the Weekenders had had their way.)
You might say that the LessWrong Solstice has no "tradition" to appeal to, or that, if anything, the weight of tradition is against the Astronomical position, considering the dates of the various solstice events over the last 10 years. But on the other hand, the self-narrative of the LessWrong Solstice is that it is by no means some late innovation, but rather a continuation of the universal and immemorial tradition of observing the winter solstice, a tradition dating back to the time of Stonehenge or further. If we accept this, then we also have to accept that the real tradition is to use the best available means to determine the date of the solstice, and observe that.
So while observing the Astronomical Solstice may be inconvenient, it represents an aspiration of what we hope the holiday might be, i.e. a commemoration of something that's important enough to be worth working your schedule around it. Holding the event on a different date (as a substitute for the astronomical date) diminishes this aspiration, as if to say that there is no room for the holiday to grow.
The LessWrong Solstice is also built on the proposition (which I agree with) that there are underexploited forms of beneficial social interaction besides the usual "sitting around talking" or "eating and drinking with a group". The distinctive mode of interaction (i.e. speeches and songs) is what sets the LessWrong Solstice apart from the usual parade of parties that dominate the December weekend calendar. And if the LessWrong Solstice is different from and complementary to these, it shouldn't try to counterprogram them by choosing its date in the same way.
(Continuing the Halloween analogy - there are always plenty of Halloween parties for adults and children to attend on the weekends of October; but the peculiar form of social interaction - i.e. trick-or-treating - must always take place on the 31st.)
The accusation of "cultiness" is what I'm most worried about. It's reasonable to suspect that a group is acting against your best interest when (1) it tries to cut you off from people outside the group, and (2) it demands of you a higher intimacy level than you were looking for. I sympathize with a general aversion to things that look like this, but as for Astronomical Solstice I might reply:
I'm also sympathetic to the "just let people enjoy things" sentiment - i.e. it's fine for different people to have different levels of investment in the community, as long there's no negativity directed at less-invested people to try and pressure them into increasing their level; but the mere possibility that this might happen isn't sufficient reason to deny the option to those who positively do want to invest more and reap the benefits thereof.
But I'm not sure. What do you think?