Hello, welcome and thank you for an interesting post!
Some very good points in your post. One additional point worth noting: Some things (can) have two-way effects.
I am going to speak from purely personal point of view, as this is a case where I certainly can't claim to speak for the WoW population, nor even the WCR population.
As time has passed by, WCR has actually become more important to me than it perhaps was in the very beginning. As those who check the top submissions page fairly often know, I have already been the at top of the all time lists for a quite a while and regularly fall into the monthly top 5, possibly even top 3 (haven't rechecked every month, so I apologize for any minor error in this statement).
I have put in a fairly large chunk of time to gather data, even on realms I don't actively play on. WCR also remembers a lot of things for me. If I need to check on my former guilds for some characters, this is where I come. Need to check someone's claims about former long term membership in a well known raiding guild on a realm I play on? I come here. Want to check someone's claims about time need to go from level x to level y? I come here.
And so on and on...
Censusplus might require a bit more work than some other applications. However, one still can't claim it's hard to use.
Protection? Yes, maybe for some people... but other people use the figures we have here as distress calls. I have seen numerous "Help, we are too few!"-style of posts on the official WoW forums... and often, WCR census data has been used to back up the claims. Sometimes correctly, sometimes less so... People don't always notice the claim about "red data" being unreliable due to too little input.
As for Blizzard and the population data. Yes, Blizzard has chosen to keep the data secret. However... there is actually multiple types of data that Blizzard hides... and what is even more interesting, they could publish some of it without having any effect on playerbase at all... If the population cap on let's say EU-Silvermoon's Horde side is 3500, 4000 or even 5000... it doesn't matter, as there rarely are more than about 150 people on even at busy times.
Also, we only see part of the activity... there isn't a single realm in the whole world that has 24/7 coverage from us... and even if there was, we still wouldn't get info on how many existing characters are currently completely inactive.
Blizzard has the passive figures, down to the accuracy of one, I believe. And it's almost certain that they have some sort of monitoring for the activity counts too. Something much easier than: "Hey, you, worker XYZ! Execute the manual /whos on realms 123, 333, 607 and 899, NOW!"
As for the sense of community... I have had the luck of finding some very nice ones even before I ever heard of Censusplus or Warcraftrealms. Also, sadly, sometimes a sense of community has a negative backlash. EU-Hakkar and EU-Crushridge are couple of fairly well known examples on the EU side. Both realms have a high number of Italian players. I have seen people kicked from groups just because they come from a certain "undesirable" realm. I have myself gotten kicked out of groups for not being able to speak Dutch, Italian, Greek, Turkish, etc. I find this very sad.
What is even more needed than a sense of community on a realm, is a sense of community as WoW players and human beings, not just as member's of a single guild, realm or nationality.
And thing is... it can work. We, here, are a living, breathing proof of that. American, Canadian, Finn, Swede, German, French, Dane, Italian, Spanish, Russian, South-African, Dutch, Israeli, Turk, Greek... both genders (Yes, there are plenty of female players out there, which I as a male player find a very good thing (female members tend to have a very positive effect on the guild chat channels)), ages from somewhere like 12 to way over 50... multiple religions, colours of skin, from those who make do with very little to those who earn thousands of dollars/euros/whatever per month.
As Rollie likes to say: "Everyone's efforts count!"... In that spirit, let's have another nice day of WoW, censuses, rest, food, sleep, love and whatever else makes your day a good one.
Epic Censi, signing off another wall of text...
The whole monthly top 10 combined totals so far a bit more than 546 000 updates... there have been months during which that figure was easily topped by a single player, on occasion more than one.
Was only 1k short on updates to reach 10th last month also... in just one day. Ok, I got more than I expected to yesterday but still, ouch? 
