They tell you where the answer can be found.
Before consulting that official answer, as a regular Luann reader but not a long-long-term fan, I was able to decode many of the individual clues, but could not give it an overall meaning. How will CIDU readers do, on either level?
Additional clue from CIDU
All the individual clues decode to the same thing.
Second additional clue from CIDU
It’s a number
Comics I Don't Understand 
OK! I do get a match for Jack Benny and the birthday candles!
I get what most of them are, but not how they are relevant to the Luann strip. I, too, am a long-time reader but not a superfan. I almost never wade through the hundreds of daily comments there.
I got one number – the birthday candles – but have no idea on any of the others. How long has Luann been running? That might be it…
jjmcgaffey nailed it @3, Luann first appeared on St. Patrick’s Day, 1985. I have no idea why, but I correctly guessed the “steps” even before I read the candles. On the other hand, I would never have figured out what Jack Benny had to do with this without the other two clues, and those three are the only ones I understand, I’m still clueless on the other five images.
P.S. If Johnny Hart had done something like this in “B.C.”, one of his riddles would have been a cross & whip.
I cheated and looked it up. I recognized a number of them, but the significance escaped me.
And good job on providing those “additional help” clues that actually were helpful yet were not at all a full spoiler.
The candles and Jack Benny were the give-away, which helped to decipher that semi-abstract picture as steps, but it took some serious Google-foo to determine why the rest of them were included. The last time I was in San Francisco was pre-Hard Rock Cafe, so I would never have figured that one out.
Some observations, encoded in ROT-13.
Fna vf Wncnarfr sbe guerr, naq Xlh vf Wncnarfr sbe avar.
Gubfr ner fgrcf? V jbhyqa’g unir erpbtavfrq gurz nf fhpu. Ohg vg ybbxf yvxr gurer ner guvegl avar bs gurz. Boivbhfyl n ersrerapr gb n abiry ol Wbua Ohpna gung unf orra svyzrq frireny gvzrf,
Gur pnaqyrf ner KKVK va Ebzna ahzrenyf, gung zrnaf guvegl avar
Wnpx Oraal’f bafperra punenpgre crecrghnyyl pynvzrq gb or guvegl avar lrnef byq. Ur arire nqzvvvgrq gb gheavat sbegl.
Gur svsgu genpx ba Dhrra’f sbhegu nyohz vf pnyyrq guvegl avar, rkprcg va ahzrenyf, abg jbeqf. V dhvgr yvxr Dhrra ohg V’ir arire urneq bs guvf bar. V unq gb ybbx vg hc.
The rest of them I don’t understand. Any help?
While I don’t have an encyclopedic knowledge of Queen songs, based on the candles and Jack Benny, I’m pretty sure I know which Queen song is being referenced (and it’s one of my favorites, about how relativity can be rough on relationships).
Thanks for those observations, Pete.
Probably the indirect answers and hinting have gone on long enough. As jjmcgaffey suggested early, this was meant to mark the anniversary of the first appearance of the strip. (They say that Greg Evans has done one of these each year.) Kilby explained this, and gave the original date, but refrained from posting the result of the subtraction: it is 39. And each printed clue can be linked to that number — for instance, the birthday cake candles show X X X I X which is Roman numerals for 39; and Jack Benny had a running joke that his age was 39.
For that explanation in their own words, and specifics on each clue, notice in the bottom right corner of the comic it says “Answer at LuannFan.com”.
While I like that it’s a very geeky song about relativistic travel by Queen’s resident Astrophysicist (he now has a PhD even!), the society in “39” has to be the most irresponsible, unplanning, unable-to-deal-with-consequences people ever: they totally wear out their planet, but apparently they are capable of sending out an expedition at relativistic speeds to scout out a new planet, but are unable to clean up the planet they have messed up; then just as all hope seems gone and they are done for, the expedition returns with news of a new place they can go mess up, hurrah! But what they failed to figure, despite being able to build relativistic travel means, so they must understand how relativity works, is that those who went out on the expedition only aged a year, while those left behind experienced many, many years and have aged to the point of death (or beyond? I can’t remember — either all the people the year-older expeditionist knew are now all old and grey, or worse, are now all long dead and gone). If you are going to volunteer for this expedition, you have to know that everyone you know will be gone by the time you get back, so either bring anyone you can’t live without with you, or don’t go, but don’t be surprised when you return!
(And yes, I totally realize that those most unplanning people ever are us, totally, both in past and sadly apparently going forward; you can claim the peoples are either like the ones depicted in films like Rapa Nui, or just straight out claim it’s us right now, polluting like there’s no tomorrow.)
Thanks very much to Pete @8 for the Japanese meaning of “San Kyu”. I had subconsiously interpreted it as a typical (German) mispronunciation of “Thank You”.
P.S. As yet unmentioned here are the “Honeymooners” (number of classic episodes) and the Constitution (number of signatures). I did look up “Survivor”, but didn’t find anything obvious, and the show is simply too repulsive for me to spend any more time on it. I am still unsure about the second to last image in the first row, but zooming in on it just now, the word on the sign might start with “PIE…”, which could be “Pier” … (which explains guero’s reference to San Francisco @7).
P.P.S. @ larK (11) – In line with your interpretation of Queen’s “39”, here’s a science fiction story from Calvin:
https://rot13.com/
@ Mitch (10) – “…They say that Greg Evans has done one of these each year…”
I do not know who “they” are supposed to be, but “they” are definitely wrong (at least as far as anniversaries are concerned). After checking a more than a decade’s worth of March 17th strips (as well as the two Sunday strips bookending each one), I did not find a single commemoration anywhere (not even an Easter egg).
P.S. I also discovered that whatever mild appreciation I ever had for Luann must have evaporated when the strip was “Batiuked” into an arduous soap opera.
OK, I see I was over-reading a message saying the strip debuted on this date and every year we feel incredibly privileged to do this. They must have meant, to do this practice of writing and drawing the strip, where I took it to mean the placement of a commemorative strip on the anniversary.
But then why pick this year to do a special? This is not the first such occasion since Karen joined the team, and despite Jack Benny and the other examples the number 39 does not really hold great cultural sway. So a meta-mystery for us.
Well, using 39 gave me a chance (@4) to lob a posthumous grenade in the direction of Johnny Hart’s evangelism, but everyone else here was far too nice to notice (or comment).