You're overthinking this. First Doses First would have been the better policy a few months ago, but in most places it just hasn't taken hold, and delivery has ramped up to the point that appointments are fairly easy to get for anyone who wants it. They're often a few weeks out, but the optimization of delaying yours by X weeks to get someone else's X weeks earlier is not worth the effort.
Get your second shot. Show everyone that getting the shots as recommended is the right general answer. Encourage standardization and avoid contrarianism and confusion, except on topics where it's egregious and clearly needed.
I agree my personal impact on FDF is small, but I'd like it to point in the right direction. I expect the impact would be less like "one person gets their shot X days earlier" and more like "X people get their shot one day earlier", though I'm not sure which of those would have the bigger effect.
As for the impact on perceptions, I'm not telling many people what I'm doing, and the people I have told don't have any vaccine hesitancy. So I'm not worried about that.
When I spoke to someone in a local Walmart pharmacy department in western Maryland a couple of weeks ago, they told me that they weren't sure if they could give a cancelled second shot to someone else, because they are sent exactly the number of shots they need on the assumption that everyone gets their second shot at 3 weeks. So do double check if that cancelled second appointment can actually be given to someone else. If it can't, there is absolutely no reason for you not to take it.
As far as going out and doing things with your spouse (or anyone else), we know that a single shot of Pfizer/BioNTech is more effective than a single shot of J&J. So unless a place is rejecting people who got J&J, I would so go ahead and present yourself as vaccinated and enjoy yourself (once two weeks have passed).
I did confirm that my slot would be available for someone else, although I can't guarantee that the slot was filled.
I have relaxed my own precautions to some extent after the first shot. I'm not too worried about being barred from anything based on anyone else's policies--the limiting factors are more likely to be my own caution, local prevalence, and whether someone else's onerous policies (general, not specific to my vaccination status) make an activity not worth doing anyway.
Do you have a reference for the comparison of first-shot Pfizer vs. J&J?
You have the right mentality, so thank you for joining a small group of people doing this. I did first dose first myself, with first dose in Jan but yesterday (about 12 weeks later) I got the second dose, because I don't know anyone who really wants it who hasn't gotten it (besides kids) and it was easy to get an appointment, and the vaccine supply is stockpiling in the US, so it's not clear to me there is any real constraint anymore. I think once it seems too easy to get a shot near you, go get the second one.
The other posters who seem to suggest your second dose was going in the trash or something are incorrect. People should have been doing first dose first for supply reasons. It's unclear if that is a reason anymore, but certainly the booster will work better at 12 weeks vs 3-4.
Closing the loop: I got my second shot at 8 weeks, on the basis that 1) I could get it as a walk-in with no wait, and 2) there's more "normal" available to go back to now.
I'm just skipping the second dose. The benefit of the second dose to a young person is almost infinitesimal.
Not getting it saves me time and the discomfort of side effects, and it reserves more doses for others, including eventually other countries. (Yes, we are still very supply constrained when you think globally.)
Clearly the second dose of pfizer/moderna increases effectiveness.
It also clearly increases the chance you're mildly sick for about a day. Probably skipping the second is fine but presumably people are keeping quiet when they do this so as to not reduce herd compliance.
I don't know about where you all are, but here the big distributor is keeping separate appointment slots for first and second doses. Putting off a second dose would just mean somebody else got their second dose, so no help there.
I got my first shot of Pfizer. They automatically scheduled my second appointment for 3 weeks later, but I canceled it, with the plan to reschedule some other time. Two reasons for this: first, while I can't unilaterally impose First Doses First, I can at least impose First Dose First--my second appointment slot was made available for someone else. Second, booster shots for other diseases are typically most effective after a longer interval.
But once vaccine supply catches up with demand, how much longer does it make sense to wait? More long-run effectiveness is good, but the booster is also more valuable while Covid is more prevalent. Eventually, vaccination will drive R below 1, even accounting for the disappearance of masks, distancing, etc. At that point, much of my protection will come from low prevalence and herd immunity rather than personal immunity anyway. There's also the possibility that Covid shots may become an annual thing like flu shots, which would also render this a short-term concern. (Or so I assume--supposing I would end up getting yet another shot later, is the timing of my second shot likely to influence the effectiveness of the third? Do memory B cells use Anki?)
In my case, it's pretty easy to continue taking strong precautions in the meantime, although my wife (who did get her second shot on schedule) will certainly appreciate when we can both go out and do things together.
[Edit: to be clear, my second appointment date had already passed before I posted this. While the other considerations raised in the comments are worth thinking about, I was specifically hoping to get some pointers to information about optimizing my own immune response, probably extrapolating from how vaccines for other diseases work since there hasn't been time to study the Covid vaccines in this much detail.]